Cognitive complexity (CC)--the ability to differentiate and integrate in a dynamic environment--has been shown to be essential to understanding complex and uncertain environments. However, educational leaders' CC has not been examined. In the current exploratory research, we examine the effect of school middle leaders' CC in relation to their Big 5 personality traits (neuroticism, conscientiousness, openness to experience, extroversion, and agreeableness) on their organizational citizenship behavior (OCB) as well as the moderator effect of CC between the Big 5 personality traits and OCB. Participants in this study were 325 educational management and leadership MA students from five higher education institutions acting as middle leaders in their schools. Results showed that a high level of differentiating CC was linked to a high level of openness to experience, extroversion, conscientiousness, and OCB. Further, high levels of integrative CC were linked to conscientiousness, openness to experience, and OCB. Low integrative CC was linked to a high level of neuroticism. Regarding the moderation effect, only integration ability serves as a moderator between conscientiousness, openness to experience, and OCB. By integrating research from both educational and noneducational literature, this exploratory study contributes to our understanding of school leaders' CC, suggesting future research avenues and implications.