The purposes of this study are as follows: (1) to determine whether burnout among elementary school teachers in Korea differs on selected demographic variables, (2) to investigate the relationship between burnout and negative mood regulation expectancies, as an internal variable, and social support, as an external variable, and (3) to examine the relative effects of these two variables on burnout. As regards burnout differences according to grades under their charge, upper-grade teachers reported experiencing a greater degree of burnout than lower-grade teachers. In particular, a significant difference was found in depersonalization. With respect to the relationships among burnout, social support, and negative mood regulation expectancies, perceived social support in general was associated with a lowered degree of burnout, while negative mood regulation expectancies correlated negatively with burnout. Furthermore, negative mood regulation expectancies, as an internal variable, affected burnout more than social support, as an external variable. This finding suggests that burnout can be alleviated by controlling negative mood regulation expectancies, and therefore, intervention efforts, such as counseling, continuing education, or training programs designed to enhance teachers' negative mood regulation expectancies, could benefit teachers in reducing their burnout.