Margrethe Vullum (born Lehmann; first married name Rode; 14 February 1846 – 14 August 1918) was a Danish-born Norwegian journalist, literary critic and proponent for women's rights.
She was born in Copenhagen, a daughter of statesman Orla Lehmann. Her first marriage was with teacher Gotfred Rode, and she was a mother of politician Ove Rode and writer Helge Rode. In 1879 she married journalist Erik Vullum.
Vullum settled in Norway in 1879, became a journalist for the newspaper Dagbladet, and later for Verdens Gang. She was a pioneering female voice in the public debates of the time. Among her contributions was a favorable review of the confiscated novel Albertine. Her interests gradually turned more into politics. She was among the principal speakers at the demonstrations in support of the Kristiania match workers' strike of 1889. She was among the founders of the Liberal Left Party in 1909.
A portrait of Vullum, painted by Oda Krohg, is located at the National Gallery of Norway.