The National Museum of Wales admitted its collections "embed historical injustice", after research showed men dominated its recent exhibitions.
Temporary exhibitions between 2016 and 2018 featured the work of 83 women compared with 273 men.
Mid Wales-based artist Shani Rhys James said there must now be a 50/50 gender split in exhibitions.
National Museum Wales director general David Anderson said he took the issue of gender balance "very seriously".
Research by BBC Wales also showed more than half of the female artists counted in the figures were in a single exhibition of photographers, Women in Focus, in 2018.
For details: https://bbc.in/2v6Up0V