This research introduces a new construct, gender-based relationship efficacy, which refers to beliefs about one's ability to relate to own- and other-gender peers. Study 1 investigated 204 fourth graders (M age = 9.56) and confirmed that own-gender and other-gender relationship efficacy represent distinguishable aspects of preadolescents' social competency beliefs that are differentially related to outcomes with own- and other-gender peers, including outcome expectancies and friendships with own- and other-gender peers. Study 2 provided further evidence of the distinctiveness of relationship efficacy for own- and other-gender peers among 403 seventh (M age = 12.48) and 453 eighth (M age = 13.50) graders and found gender and age differences. Developmental changes and implications for research on intergroup relationships are discussed.