Teachers' well-being and self-efficacy are two important factors linked to quality education. Recent research examining their bidirectionality has revealed inconsistent findings, while those examining the relationships among pre-service and in-service teachers are scarce. This study investigates the reciprocal relationships between teachers' well-being and self-efficacy in a sample of Hong Kong early childhood education teachers. Participants were 155 pre-service (n = 77) and in-service (n = 78) teachers (M[subscript age] = 23.97, SD = 4.46, female = 92.9%). Participants reported their teachers' well-being (PERMA model including positive emotion, engagement, relationship, meaning, and accomplishment) and teachers' self-efficacy at two-time points. The results from the cross-lagged panel model revealed that teachers' self-efficacy at baseline significantly predicted all aspects of prospective well-being except for engagement. In contrast, none of the teachers' well-being components significantly predicted later teachers' self-efficacy, except for accomplishment. The associations between teachers' self-efficacy and well-being were invariant across pre-service and in-service teachers. The results underscored the importance of teachers' self-efficacy in facilitating teachers' well-being. The findings also highlight the utility of intervention efforts targeting teachers' self-efficacy and well-being, especially in promoting teachers' accomplishment, at an early stage of their careers.