Most countries of the world have still not succeeded in achieving the equal participation of women and men in parliament, including Croatia and Serbia. The aim of the paper is to compare how the number of women in the Croatian and Serbian parliaments changed from the first multi-party elections in 1990 to 2016, with an emphasis on the 1990, 2000 and 2016 elections. The research question is which legislative and social aspects contributed to the different percentage of women in the parliament of the Republic of Croatia and the Republic of Serbia in the period of 26 years? The temporal analysis was used. Both Croatia and Serbia are signatories to various international documents that promote equality and the fight against discrimination, guarantee gender equality with their constitutions, both of them have enacted changes in legislation and introduced quotas, but ultimately have different percentages of women in parliament. Although there is a lot of criticism about quotas, respecting quotas is of great importance in order to reach a larger number of women in parliament and to make them a "critical mass". Legislative and social aspects that contributed the most to the different percentage of women in the parliaments of the Republic of Croatia and the Republic of Serbia in the mentioned period are legally determined quotas, sanctions for non-compliance, electoral and party system of the state and in some years cooperation of women in politics with other non-governmental organizations. There are stricter sanctions in Serbia for non-compliance with quotas and more precise laws related to candidate lists, which ultimately affects a larger number of women in parliament. However, Serbia still has much room for improvement. Women mainly work in committees focused on human rights, protection, and social policy, but it is important for their number to increase in other committees where they are currently only a minority and that they take leading positions in parties. Only a part of the factors that affect the final percentage of women in parliament has been researched in this paper, however, there is still much room for further research.