ABSTRACT We explored the relationship between teachers’ perceptions of transformational leadership and organisational citizenship behaviour (OCB) in Taiwan’s six-year high schools and whether work engagement moderated the relationship between the principal’s transformational leadership and teachers’ OCB. A total of 310 valid questionnaires were collected from teachers in Kaohsiung City, Taiwan. The six-year high school teachers’ perceptions of principals’ transformational leadership and work engagement were at the upper-middle level, with the sub-dimensions “inspiration and encouragement”, “focus”, and “dedication” ranking the highest. Their OCB was high and the sub-dimension, “active and helping behaviour”, ranked the highest. They felt that the principal’s transformational leadership, work engagement, and teachers’ OCB had a significant positive relationship and explanatory power. Their work engagement positively moderated principals’ transformational leadership and OCB. If the principal focused on transformational leadership and matched teachers with higher degrees of work engagement, a higher OCB of teachers would appear.