Sisowath Sirik Matak (Khmer: ស៊ីសុវត្ថិ សិរិមតៈ; 22 January 1914 – 21 April 1975) was a Cambodian politician and member of the Cambodian royal family, under the House of Sisowath.

Sirik Matak was mainly notable for his involvement in Cambodian politics, particularly for his involvement in the 1970 change in power against his cousin, then Prince Norodom Sihanouk, and for his subsequent establishment, along with Lon Nol, of the Khmer Republic. In April 1975, Sirik Matak was executed by the orders of Angkar, shortly after the Khmer Rouge seized power in the capital Phnom Penh, where he and other government officials were captured and executed by the new regime.

Sirik Matak was born in Phnom Penh, and was a member of the Sisowath family, being the great-grandson of Sisowath of Cambodia by his grandfather Sisowath Essaravong and his father Sisowath Rathary. He was recruited into the colonial civil service in 1930.

Under the colonial French-imposed constitution, any member of the Norodom or Sisowath branches of the family could be selected as king, and Sirik Matak was therefore one of the possible contenders to the Cambodian throne. In 1941, after the death of King Sisowath Monivong, the French authorities selected Sirik Matak's cousin Norodom Sihanouk to be King, believing him to be relatively pliant. Sihanouk later accused Sirik Matak of harbouring a deep resentment against him, stating that he "hated me from childhood days because he thought his uncle, Prince Sisowath Monireth, should have been placed on the throne instead of myself. He even had a notion that he himself should have been chosen".

After the Second World War and capitulation of Japan, Sirik Matak became increasingly involved in Cambodian politics. As a part of the right-wing Khmer Renovation party headed by Lon Nol, he took part in the National Assembly elections in 1947, though the party failed to win any seats. Sihanouk, then acting as Prime Minister, placed him in charge of defence in 1952, formally appointing him Minister of Defence in the interim government set up after independence according to Geneva Accords in 1954; Sihanouk's Sangkum movement absorbed the Khmer Renovation Party prior to the Sangkum victory in the 1955 elections.

Despite the incorporation of much of the right-wing opposition into the Sangkum, Sirik Matak remained an implacable opponent of Sihanouk, and especially of the latter's toleration of North Vietnamese activity within Cambodia's borders. Throughout the 1960s, Sihanouk attempted to minimize Sirik Matak's leverage on domestic politics by successively appointing him as Ambassador to China (1962–1964), the Philippines, and Japan.

Sirik Matak's power increased substantially after Lon Nol became prime minister in August 1969. After being appointed as Lon Nol's deputy, he proceeded to organise a series of economic denationalisation and deregulation measures in opposition to Sihanouk's previous policy of state control of import and export, banking, and production of pharmaceuticals and alcohol. Sirik Matak even visited Hanoi secretly to find out what could be done to remove North Vietnamese troops from Cambodian soil. He was infuriated when he was shown documents signed by Sihanouk agreeing to the establishment of North Vietnamese bases and the transport of Vietnamese supplies through Cambodian ports.

On 12 March 1970, while Sihanouk was on a trip abroad, Sirik Matak canceled Sihanouk's trade agreements and Lon Nol demanded that all North Vietnamese and NLF troops leave Cambodia by dawn on March 15. The deadline passed without any response from the Vietnamese. On 18 March, Sirik Matak assisted Lon Nol in organising a vote of the National Assembly to depose Sihanouk as head of state. The pretext was given by a series of anti-Vietnamese riots – likely encouraged by the Prime Minister and his deputy – in front of the North Vietnamese embassy.