Research in clinical supervision has primarily focused on the contribution of supervisors to training outcome. However, peers may also play a significant role in trainees' development, particularly during group supervision. Fifty-three trainees from 10 supervision groups completed measures of peer relationship, supervisory working alliance (SWA), supervision satisfaction (SAT), and counseling self-efficacy (CSE) at three time points during a 20-week counseling practicum at a department clinic in Hong Kong. Multilevel modeling was conducted to test the hypothesis that both peer relationship and SWA contribute to SAT and CSE. The path model results showed that higher within-and between-trainee SWA was associated with higher SAT, and higher between-trainee SWA was associated with higher CSE. Better within-and between-trainee peer relationship was associated with higher CSE, but not with SAT. Thus, when peer relationship and SWA were entered as predictors into the same analysis and allowed to control for each other's effects, they each have unique contributions to the outcome of group supervision. Implications for training and supervision research are discussed. Public Significance StatementClinical training often takes place in groups. This study provides evidence that supervisors and peers have unique contributions to training outcomes in group supervision. This study lends support to the recommendation that when designing training programs, attention should be paid to the quality of peer relationships in addition to supervisory relationships.