Parelius Meyer Mentsen (1 October 1902 – 22 April 1985) was a Norwegian trade unionist, who served as leader of the Norwegian Confederation of Trade Unions (LO) from 1965 to 1969. Mentsen was born in Ballangen, Ofoten. He was a timberer by education and occupation, but soon joined trade union and the Norwegian Labour Party in Narvik. He became secretary of the trade union (Samorg) in Finmark in 1936 and worked at the Tromsø office of Confederation of Trade Unions from 1940. In 1946 he was elected secretary of the Confederation of Trade Unions with office in Oslo.