Teacher leadership has recently gained significant attention in the literature since there is enough evidence that it leads to effective student outcomes. Therefore, many scholars study the antecedents of teacher leadership. This study investigates the impact of self-affirmation on teacher leadership beliefs through an experimental design. Self-affirmation, a well-established construct in psychological science, refers to participants' affirming their self-transcendent (e.g., empathy, justice, honesty) or self-enhancement (e.g., power, status, wealth) values through a writing exercise. In the experiment (n=221), participants were randomly assigned to one of three groups: a self-transcendent value-affirmation group (STVA), a self-enhancement value-affirmation group (SEVA), or a control group. Participants in three groups wrote about their self-transcendent values, self-enhancement values or their meals and completed teacher leadership belief scale. Analysis of variance (ANOVA) demonstrated that the STVA group had significantly higher scores on teacher leadership belief scales compared to the SEVA and the control group. This finding suggests that affirming self-transcendent values can lead teachers to adopt leadership beliefs, which in turn is likely to affect their leadership behaviours. School leaders can incorporate self-affirmation exercises into professional development programmes to facilitate teacher leadership.