Abstract: Purpose – Social media have become an increasingly important venue for prosocial campaigns. Competing for the public’s attention in the digital space is an ongoing challenge. This study aims to test the influence of ad-context congruence, ad position and ad type (i.e. public service advertising [PSA] vs cause-related brand [CRB] advertising) on the effectiveness of prosocial native advertising on social media. Design/methodology/approach – Two experiments were conducted on different social media platforms (i.e., Twitter and Instagram) with varied prosocial issues (i.e., healthy eating and environmental sustainability). Findings – Experiment 1 indicated that the congruence between prosocial native ads and social media feeds elicited greater ad involvement and a more favorable ad attitude, regardless of ad position. Experiment 2 revealed that such an impact was contingent on whether the prosocial native ad was a public service ad or a CRB ad. The positive influence of ad-context congruence was pronounced among public service ads but was not observed among CRB ads. Perceived ad involvement mediated the interaction effects between ad-context congruence and ad type on ad attitude and behavioral intention. Originality/value – The study extends ad-context congruence research to the context of prosocial native advertising on social media. Moreover, it identifies ad type as a boundary condition for the congruence effects and reveals that increased ad involvement is the mechanism underlying the positive effect of congruent PSA.