Purpose: The aim of this study is to explore the relationships between dimensions of teacher efficacy and affective well-being while focusing on the roles of demographic characteristics (gender, grade level, educational background, and seniority). Design/Approach/Methods: 1,115 primary and 541 secondary school teachers in Hong Kong participated in the questionnaire survey. A series of t-tests, ANOVA, correlation analysis, and hierarchical multiple regressions were conducted. Findings: The younger teachers reported lower scores for well-being and efficacy than their senior counterparts, and the female and primary school teachers reported significantly higher levels of teacher efficacy for student engagement than their respective counterparts. Of the dimensions of affective well-being, pleasant affect was more closely related to teacher efficacy than negative affect, and the activated pleasant dimension of enthusiasm had the strongest influence. Of the three dimensions of teacher efficacy, efficacy for student engagement was most strongly associated with affective well-being. Originality/Value: The study revealed that teachers' affective well-being is not only important in itself, but also contributes to classroom teaching. The enthusiasm and passion possessed and maintained by teachers could play important roles in enhancing their self-efficacy. Furthermore, maintaining a good affective well-being status and even a modest level of anxiety contributes to their efficacy for student engagement, a dimension on which teachers reported the least confidence. Suggestions were put forward on how to improve teacher efficacy and well-being.