Nong-O Sit Or (น้องโอ๋ ศิษย์ อ.) was born as Arphichet Kotenan in Sakon Nakhon Province in Northeastern (Changwat) region of Thailand. He had his first fight at the age of 14.
On August 3, 2008, Nong-O fought against Kōji Okuyama at Keio Plaza hotel in Hachiōji, Tokyo, and he won by KO with left elbow strike during 3rd round. December 9, 2008, he fought against Wutidet Lukprabath at Lumpinee Stadium in the memorial event of Lumpinee Stadium establishment. He won by decision after 5th round.
On January 18, 2009, Nong-O fought against Tomoaki Suehiro at Yoyogi National Gymnasium for the Muay Thai event "Muay Lok", and he won by TKO because the referee stopped the contest after he knocked down Suehiro twice with eight hook and left hook during 1st round. After the contest, he was given a bunch of flowers by Shinya Aoki. Nong-O was going to fight against Shunta Itō in the beginning, but he was replaced because his legs had not been healed enough.
On November 8, 2009, he fought against Trijak Sitjomtrai in Japan. Trijak was the current champion at featherweight sanctioned by Professional Boxing Association of Thailand, but Nong-O won by majority decision(2-0) after 5th round.
On December 8, Nong-O fought against Petboonchu F. A. Group for his title of Lumpinee Stadium at Super featherweight(130 lbs). Nong-O won by decision and became the new champion.
On January 17, 2010, Nong-O participated the tournament of "Yod Muay Champions Cup 60kg" in Japan. He fought against Sindam Kietmukao at the first match. After 5th round, the bout was resulted draw as 1-0. Nong-O lost by the split decision after extra round (6th round). On December 9, He challenged Saenchai's titles of Lumpinee Stadium and WMC, but he lost by decision.
On January 19, 2011, Nong-O Sit Or was named 2010 boxer of the year at the Society of Friends of Sportswriters Awards Night in Bangkok.
Nong-O started the year with a win over Singdam in February and followed it up the following month with another win over F16 Rajanon. He then lost a very close fight to Singdam in May, which many fought Nong-O had done enough to win, but beat Petboonchu FA Group in June. On 31 July he fought Singdam in the main event at Lumpinee Stadium and was defeated by unanimous decision.
He will face Petboonchu F.A. Group for the seventh time on October 12, 2012 at Rajadamnern Stadium.
He TKO'd Mongkolchai Phetsupaphan in five on February 7, 2013.
He beat Singdam Kiatmuu9 on points to win the Lumpinne lightweight belt on June 7, 2013.Muaythai
2014 Rajadamnern Stadium Lightweight champion
2013 Lumpinee Stadium Lightweight champion
2012 Thailand Lightweight (135 lbs) champion
2011 Toyota Vigo Marathon Tournament (130 lbs / 59 kg) champion
2009 Lumpinee Stadium Super Featherweight (130 lbs / 59 kg) champion
2007 Lumpinee Stadium Featherweight champion
2006 Lumpinee Stadium Junior Featherweight (122 lbs / 56 kg) champion
2005 Thailand Bantamweight champion
2 times Thailand Junior Featherweight (122 lbs / 56 kg) champion
2010 Muaythai boxer of the year (Society of Friends of Sportswriters)
2005 Muaythai boxer of the year