The Women 50:50 campaign, which is calling for fair representation of women in public life, said women make up 13 of the 59 people who have been appointed government special advisers since the parliament opened in 1999.
The first parliamentary session under Labour MSP Donald Dewar had no female special advisers, while during the Labour and Liberal Democrat coalitions women accounted for six out of 31 of the posts, or 19 per cent.
The SNP has had seven female special advisers out of 28 (25 per cent) and a third of those appointed to advise First Minister Nicola Sturgeon are women.
Talat Yaqoob, campaign co-founder, said: “Having women at every level of politics in Scotland is the only way we can ensure real representation and inclusiveness, but we need them beyond the chamber.
“The influencers behind the scenes are, in the main, men, we need women in these positions influencing policy and decision-making.”
The campaign and Scottish Labour leader Kezia Dugdale are holding a panel debate on the lack of female staff in politics.