Agda Montelius née Reuterskiöld (23 April 1850 in Köping – 27 October 1920) was a Swedish philanthropist and feminist.
Montelius was the daughter of the government minister and noble General-Lieutenant Alexander Reuterskiöld and Anna Schenström and married professor Oscar Montelius in 1871. She was active within several organisations: chairman of Maria skyddsförening (The Maria Protection Society), in Nya Idun (New Idun) and in Föreningen för välgörenhetens ordnande (The Society of organised Charity) as well as managing director of its central committee in 1889–1911. She also belonged to the Sällskapet för uppmuntran av öm och sedlig modersvård (The Society for encouragement of tender and decent Motherly care) and was the first female chairman of the head feminist organisation Fredrika-Bremer-förbundet (The Fredrika Bremer Association), where she had been a board member since 1886, in 1903–1920 and a board member of Svenska fattigvårdsförbundet (The Swedish Society of Poorcare).
She was given Illis Quorum in 1910.