Although a catalog of beluga socio-sexual behavior has been established, to date, little is known about the development of beluga (Delphinapterus leucas) socio-sexual behavior. The present study explored how socio-sexual behavior developed in belugas under human care by recording the behavior of 5 belugas between years 4 and 10 of life. Overall, the presence of young male conspecifics was the most influential predictor of whether or not the subjects engaged in socio-sexual behavior, and social networks particularly emphasized the relationships between males in the social group. The subjects of the present study were also more likely to be involved in socio-sexual behavior as they matured and were more likely to be involved if they were male. Additionally, specific socio-sexual behaviors of the repertoire, including horizontal s-postures and pelvic thrusts, increased in prevalence throughout development. These findings have implications for conservation efforts as social group composition may contribute to the development of socio-sexual behavior, which in turn may influence the reproductive success of beluga populations. Furthermore, because socio-sexual behavior composes a substantial portion of a beluga's activity budget and the majority of the time spent socializing, it is likely crucial for social bonding and well-being in belugas, especially males.