<p>Group gender composition is a critical characteristic that influences both group perceptions and group performance. However, its effects on intergroup evaluations and interaction willingness remain underexplored. Across two studies (Study 1, <i>N</i> = 100; Study 2, <i>N</i> = 205), we manipulated the gender composition of four-person groups to investigate its impact. Our findings revealed that group gender composition significantly shaped perceptions, with male-majority groups being perceived as more agentic and competitive, and female-majority groups as more communal. Notably, we identified an intergroup gendered homogeneity effect, where individuals demonstrated enhanced evaluations, stronger gender-stereotypical perceptions, and greater willingness to cooperate with outgroups that shared similar gender compositions to their ingroup. This effect persisted even under competitive conditions, highlighting its robustness. These findings highlight the importance of group gender composition in shaping intergroup dynamics and reveal how gender composition similarity fosters more favorable intergroup attitudes and cooperation.</p>