In the aftermath of civil conflict, war-torn states often require reform of their government institutions. Gender balancing, or the inclusion of more women in security-sector institutions, is an increasingly common reform incorporated into state-building processes. Our theoretical priors suggest that gender balancing may influence unit cohesion, operational effectiveness with respect to sexual and gender-based violence, and organizational gender norms. We study these propositions using laboratory experiments with police officers of the Liberian National Police (LNP). We randomly assigned the proportions of women and men in 102 groups of six LNP officers to observe their deliberative processes and group choices. In our experiment, adding more women increased unit cohesion, but we find no evidence to suggest that simply adding more women would increase group (or individual) sensitivity to sexual and gender-based violence. We also find that, despite an increase in participation and influence by women, male beliefs about women’s role in policing do not improve with the inclusion of women. As one of the first experimental studies to assess the effects of gender composition within the actual population of interest, our results shed light on how international interventions to address gender equality in postconflict countries affect important outcomes related to security.