Ragna Vilhelmine Nielsen (née Ullmann) (17 July 1845 – 29 September 1924) was a Norwegian pedagogue, school headmistress, publicist, organizer, politician and feminist.

Ragna Nielsen was born in Christiania (now Oslo) to Jørgen Axel Nicolai Ullmann and his wife, pedagogist, publicist, literary critic and feminist Cathrine Johanne Fredrikke Vilhelmine Dunker.

[1] She established the school Fru Nielsens Latin- og Realskole in Kristiania in 1885.

She was engaged in the spiritualism movement and a co-founder of Norsk Selskap for Psykisk Forskning in 1917.

Among her books are Norske kvinder i det 19de aarhundrede from 1904, Fra de smaa følelsers tid from 1907 (published anonymously), and Sisyphos og de politiske partier from 1922.