Previous studies differed largely in their findings concerning the relationship between principal leadership and students' mathematics achievement because of the complexity of principal leadership. As Hallinger and Heck's theoretical framework showed, principal leadership was comprised setting vision/goal, school management, and school climate maintenance. This paper used TIMSS 2011 data collected from 3,961 fourth-grade students and 197 school principals in Germany and 4,138 students and 150 school principals in Chinese Taipei from a comparative perspective to explore the conceptual constructs of principal leadership based on principals' work time allocation via confirmatory factor analysis (CFA), the effect of principal leadership in general and its various dimensions on students' mathematics achievement via multilevel structural equation modelling (MSEM), and the principal leadership styles via latent class analysis (LCA). In conclusion, principals in Germany and Chinese Taipei shared similar ideas about principal leadership in primary schooling. However, the effect of principal leadership in predicting students' mathematics achievement differed largely between the two economies, which might be related to the differences in their principals' leadership styles. Theoretically, future studies should pay more attention to the various dimensions of principal leadership than its effect in general in their exploration of students' mathematics achievement.