While recent studies found women frequently behaving more sustainably than men, few studies investigated interventionsmotivatingmen to act (more) proenvironmentally. According to the precarious manhood hypothesis, men may be less motivated because they consider sustainability as a feminine attribute threatening their male identity. We conducted a pilot study (N= 165) to determine which proenvironmental behaviors are indeed perceived as more feminine versus masculine. Two subsequent preregistered main studies (N₁= 281, N₂= 226) tested experimental interventions designed to motivate men to behave more proenvironmentally in a 4 (condition)× 3 (time:T₁ vs. T₂ vs. T₃) design. Male participants were randomly assigned to either a control or to one of two intervention conditions. The intervention conditions attempted to motivate men to behave more proenvironmentally with pictures and self-reflection exercises. In Study 1, the pictures consisted of men engaging in (a) feminine behaviors (e.g., wearing a dress) or (b) feminine sustainable behaviors (e.g., picking up trash). In the intervention conditions, men’s scores increased for some sustainability measures. Replicating prior studies, however, women generally scored higher than men on all sustainability measures, regardless of condition. In Study 2, our updated interventions consisted of a dynamic norm message and pictures of men engaging in allegedly (a) feminine (e.g., buying regional food) or (b) masculine (e.g., installing water-efficient appliances) sustainable behaviors. Men in both intervention conditions significantly increased their proenvironmental behavioral intentions from T₁ to T₂. Mediation analyses suggest that antifemininity explained the gender disparity in sustainability in both studies.