Pierra Vejjabul (Thai: เพียร เวชบุล, born Pierra Hoon, 27 November 1898 – 1984) was the first female physician of Thailand.
Pierra was born in Lampang, Thailand to Trongkij Hoontrakul, a well-to-do merchant, and Phant Hoontrakul, who was his third wife. She was the last child of the family. She was educated in Bangkok at Saovabha and Saint Joseph Convent Schools, and graduated from secondary school in 1925. She then took up a teaching position at Assumption Convent and Saint Joseph Convent Schools.
Inspired to study medicine by a French doctor who helped her mother, upon graduation Pierra had applied for training at the Medical School at Siriraj Hospital, but was rejected as the school did not accept females at the time. At the age of sixteen, against her father's wishes, she left for Saigon, where she studied French for one year with the support of Catholic nuns. She then left for France, where she obtained a medical education at the University of Paris, graduating in 1936 and then returning to practise in Thailand.
Under her influence, prostitution was outlawed by the Thai government in the early 1960s.
She later took a position in the Thai Ministry of Public Health's Department of Venereal Diseases.
She later adopted the surname Veijjabul, which was granted by Princess Mother Srinagarindra during the premiership of Plaek Pibulsonggram.