The film opens with a recap of earlier events in the series as David Sloan writes a letter to his wife, Vicky. After being framed for murder by Tong Po, Sloan has spent the last two years in prison, while his wife has become the sexual captive of his old nemesis, who has since become one of the most powerful drug lords in Mexico.
After receiving explicit photos from Po of his kidnapped wife, Sloan takes his frustrations out on a fellow prisoner before meeting with a DEA official, Casey Ford (Nicholas Guest), who briefs Sloan about their situation. He reveals that the agency has been unable to apprehend Po by their own means and that Po intends to host a martial arts tournament at his private compound, with the winner earning a match against Po and a $1,000,000 cash prize. Knowing the history between them, Casey offers to release Sloan if he will enter the tournament and eliminate Po himself. Sloan eagerly accepts, using the alias "Jack Jones" to conceal his identity. His first stop is a street fight, where he easily dispatches two street fighters earning him a necessary invitation from a man named Brubaker, who scouts fighters and invites them to Po's tournament.
On his way to the border, Sloan enters a roadside bar and stumbles upon a group of thugs harassing a young woman named Megan Laurence. Sloan defeats them with ease and saves the woman, who is ungrateful for his help and reveals that she is entering the tournament as well. Sloan arrives at the compound and is greeted by Darcy Cove, one of Po's many female sex slaves, who tells him that he must compete in the qualifying matches. Sloan witnesses Thomas, a brutal fighter, take out another young fighter. Then, Sloan is chosen to face Laurence. Reluctant to harm the young woman despite her taunting, Sloan peacefully subdues her. He also meets up with an old acquaintance named Lando Smith, a talented fighter who turns out to be his backup on the mission.
At the party of the tournament's seventh anniversary, Bill, Po's right hand man, introduces Tong Po to the crowd. Sloan leaves the party soon after to search for his wife, but finds the entire compound to be heavily guarded. Meanwhile, Po offers Laurence a second opportunity to compete, but places a bounty on her head inciting all the other fighters to attack her at once. Laurence holds her own until Po attacks her, prompting Lando to intervene. After a brief standoff with Po, Lando escorts Laurence back to her room.
That night, Sloan searches the compound and manages to locate his wife, but is unable to free her before the alarm sounds. On Po's orders, the guards try to apprehend him, but they fail and Sloan escapes. The next morning, Sloan befriends Laurence and offers his help for the upcoming tournament.
The tournament begins with several matches taking place. Sloan witnesses Thomas incapacitate a female judoka fighter (Dana Dru Evenson), while Lando and Laurence both win their respective matches. When Sloan (as "Jack Jones") is called up to fight, Lando approaches Darcy to divert Po's attention away from him. Sloan wins his fight quickly and escapes Po's notice.
In an effort to gain more intelligence about Sloan's wife, Lando enters a romance with Darcy and presses her for information while offering to help her escape from Po. Darcy provides him with the necessary intel which he passes on to Sloan before being caught by Bill and his guards. Po tortures Lando to learn why he has come to the tournament, but unable to get a satisfactory answer, he brings forth Darcy and tortures her in front of Lando forcing him to admit that he is a DEA agent. Lando pleads for Darcy's life, but Po tortures her to death.
Meanwhile, Sloan seeks to free his wife, but is unable to find her since Po had her moved from her original cell as a result of his previous intrusion. Sloan is then captured by Po, who is surprised to see his old rival. On the final day of the tournament, Po declares that all fights will be to the death and dismisses several fighters who are unwilling to risk their lives, but shoots them all dead as they depart. The tournament proceeds with even more fighters killed at the hands of their opponents, until both Lando and Sloan are dragged into the arena.
Po announces that the tournament is a memorial to his late wife, Sian, who was killed five years prior when the DEA invaded his home. He blames Sloan for her death and offers a $500,000 bonus to whoever is able to defeat Sloan. Thomas accepts the challenge, but Sloan is able to defeat him. Po calls for more challengers, and the other two remaining fighters step forward. One after the other, Sloan proves to be more than a match for them. In frustration, Po orders Laurence to fight him, but she refuses, calling him a coward. Po threatens to kill them all if she does not fight, but Laurence asserts her belief that there was never any prize money and that Po intends to kill them all regardless, her words prompting the other fighters to rally against him. As one, the men rise up to fight for their lives against Po's armed guards.
The fighters seem to have a strong advantage, until Po himself enters the fray and begins to subdue them. Though he fights bravely, Lando is easily bested by the Muay Thai master. In the end, only Sloan and Po are left standing. After a brutal confrontation, Sloan conquers his rival once again, but Bill takes Vicky at gunpoint giving Po the opportunity to escape. Sloan dispatches Bill with a well-aimed knife throw before he and Vicky exit the compound along with Lando and Laurence.Sasha Mitchell as David Sloan
Nicholas Guest as Casey Ford
Brad Thornton as Lando Smith
Thom Mathews as Bill
Kamel Krifia as Tong Po
Michele Krasnoo as Megan Laurence
Deborah Mansy as Vicky
Jill Pierce as Darcy
Nicholas Anthony as Brubaker
Derek Partridge as Mexican Bob
Burton Richardson as Thomas
Dana Dru Evenson as Judoka Dana
MarkAnthony Baca - Stuntman
Jean-Claude Van Damme as Kurt Sloane (archive footage)
Dennis Alexio as Eric Sloane (archive footage)
Michel Qissi as Tong Po (archive footage)
TV Guide rated it 2/5 stars and wrote, "Kickboxer 4 does proud by the franchise that gave the world Jean-Claude Van Damme." Adam Arseneau of DVD Verdict called it an improvement over the third film but still bad. In 2012, Brian Tremml of Paste included it their list of "The 25 Most Awesomely Bad Movies on Netflix Instant".