As competition increases, organizations rely more on employees who go beyond the job requirements stipulated in their contractual agreements. Therefore, there is a call for Organizational Citizenship Behavior (OCB). Employees who demonstrate organizational citizenship behavior identify themselves with their organization and are willing to go the extra mile to improve organizational performance. In cognizant of this, several scholars are attracted to investigate Organizational Citizenship Behavior (OCB). This study attempts to determine the effect of Organizational Citizenship Behavior on organizational performances in the context of Ethiopia's private higher education institution by taking St. Mary's University as a case. The target population of this research is the academic staff of the university. A sample of 150 academic staff was selected by employing a simple random sampling technique to collect data through a questionnaire, and 15 department and faculty deans were interviewed. An explanatory design along with a sequential mixed approach has been employed to meet the study objectives. The research findings revealed that altruism, conscientiousness, sportsmanship, and civic virtue behaviors positively and significantly predict organizational performance in higher education. Altruism is found to be the most significant behavior that influences organizational performance in higher education.