Knowledge sharing is an important organizational resource and should be encouraged in the field of teaching. We used a cross-sectional design, and 796 teachers in primary or secondary schools completed measures of the Big Five personality traits, burnout, and knowledge sharing. The results showed that (a) in the regression model, the traits of extraversion and agreeableness were positively associated with knowledge sharing, but conscientiousness, openness, and neuroticism were not significant in predicting knowledge sharing; (b) burnout was negatively associated with knowledge sharing after controlling for personality; and (c) burnout moderated the relationship between personality and knowledge sharing; that is, compared with those with a high score for burnout symptoms, the relationship between personality and knowledge sharing was stronger for those with a low score for burnout symptoms. The results suggest that interventions aimed at reducing teachers burnout might be helpful for improving their knowledge sharing.