This paper investigates gender-based differences in cooperativeness among French parliamentarians by analyzing legislative behaviors, such as cosponsorship and voting patterns. Using a comprehensive dataset covering all bills and amendments authored in France’s Lower House between 2012 and 2022, we show that female parliamentarians attract fewer cosponsors, particularly from members of their own parties, despite being more likely to support their colleagues’ initiatives and exhibit higher voting participation. This asymmetry highlights a paradox: while female legislators display greater cooperative and altruistic behaviors, they receive less reciprocal backing, limiting their legislative influence. The observed patterns are driven by behavioral gender differences rather than differences in observable characteristics, thematic alignment, or the quality of the politicians.