This research investigates the impact of supportive supervisors on doctoral students' research productivity, with parallel mediation effects of academic engagement and academic psychological capital as two mediators. Data has been collected through an online survey from international doctoral students (N = 415) studying in six research-oriented universities in mainland China. Confirmatory factor analysis and structural modeling were used in the analysis and mediation analysis conducted by adopting the 04 Model in PROCESS. The results indicated that a supportive supervisor is positively related to research productivity. Student psychological factors--academic engagement and academic psychological capital--partially mediate the relationship between supportive supervisors and research productivity. The findings suggest that the supervisor's supportive behavior is essential for encouraging students' academic engagement and academic psychological capital. Furthermore, students are more productive, and their engagement and psychological resources are increased under supportive supervision, which ultimately significantly increases their research productivity.