This study examined teacher perceptions of principals' social justice leadership and their effect on teachers' academic optimism in Taiwan, along with the moderating effects of teachers' gender, position, and school size. While a total sample of 1,470 elementary and secondary school teachers were surveyed, this study applied a multidimensional framework to examine social justice leadership. The results indicate that teachers perceive principals' social justice leadership to a high degree. Second, teachers' perceptions of social justice leadership significantly vary by gender, position, and school size. Third, social justice leadership positively relates to teachers' academic optimism. Fourth, gender has a moderating effect on the relationship of social justice leadership and teachers' academic optimism, which suggests that the practice of principals' social justice leadership is influenced by the inherent culture, at least to an extent.