Purpose: This study aimed to examine the influence of psychological capital on the students' academic success in a PhD journey in Tanzania. Design/methodology/approach: A cross-sectional survey design was used and data were collected through structured questionnaires from 200 PhD students in Tanzania. Confirmatory factor analysis was used to test the measurement model. The hypotheses were empirically tested using structural equation modeling (SEM). Findings: The findings affirm that psychological capital in terms of hope, self-efficacy, resilience and optimism are significant predictors of students' academic success in a PhD journey. Originality/value: To the best of the authors' knowledge, this paper is among the first to comprehensively examine the influence of psychological capital on students' academic success in PhD studies. Previous studies have primarily focused on the undergraduate level. Additionally, this study extends the applicability of conservation of resource (COR) theory to the context of PhD students, demonstrating that psychological capital serves as a crucial resource for them to achieve success in their PhD studies.