Martha Emily Larsen Jahn (17 April 1875 – 2 August 1954) was a Norwegian peace and women's activist. She was born in Christiania as a daughter of wholesaler Christian Larsen (1842–1905) and Sanda Plate (1851–1879). In April 1911 she married Gunnar Jahn, politician and director of Statistics Norway. She died in August 1954 in Oslo.