Prince Phetsarath Ratanavongsa (Somdej Chao Maha Oupahat Pethsarath Ratanavongsa lit: His Highness (the) Vice-King Phetsarath Ratanavongsa) (Lao: ເພັຊຣາຊ; 19 January 1890 – 14 October 1959) was the 1st Prime Minister of Laos from 8 April to 20 October 1945, and was the first and last vice-king of the Kingdom of Laos.
He was born on 19 January 1890 in Luang Prabang, the second son of Oupahat Bounkhong and his second wife, Princess Thongsy. As the country's last oupahat, he became a leading figure of modern Laos. He established the system of ranks and titles of the civil service, promotion and pension plans, and created a Lao consultative assembly, reorganized the king's Advisory Council. Phetsarath reorganized the administrative system of the Buddhist clergy, and established a system of schools for educating monks in Pali. He created the Institute of Law and Administration to train entry level officers (Samien) who would then move up the ladder as Phouxouei, Chao Meuang, and Chao Khoueng successively. He set up rules to reward, reassign, and promote deserving civil servants, and created the judicial system, including civil and penal codes.
In part because of his popularity and in part because of his perceived saksit power, many Lao people hang his picture in their homes.