Although various studies have been carried out on the relationship between attachment and prosocial behavior, less research has focused on the mediating role of pair attachment in the university population. For this reason, the study aims to evaluate the mediating role of pair attachment in the relationship between parental attachment and the prosocial behavior of Chilean university students. The participants were 198 university students, of which 76.3% indicated being female (n = 151), 23.2% male (n = 46), and 0.5% other gender (n = 1). To measure parental and pair attachment, the Parent and Pair Attachment Inventory was used in its version adapted to Spanish (Delgado et al., 2016), and prosocial behavior was measured with the Prosociality Scale (Caprara et al., 2005). Descriptive and correlation analyses will be used to analyze the data. The evaluation of the mediating role of pair attachment was carried out using the Bayesian method, considering Monte Carlo techniques with Markov chains (MCMC) and 20,000 iterations. The results showed that pair attachment partially mediates the relationship between parental attachment and prosocial behavior. It is inferred that when the pair attachment intervenes, a greater effect of the parental attachment on prosocial behavior is observed. It is concluded that pair attachment constitutes a psychological mechanism that contributes to the development of prosocial behavior.