This study investigates whether personality and grit affect the Organizational Citizenship Behavior (OCB) and if so, whether this relationship is mediated by job involvement or not. This study was a survey at the Industrial Vocational Higher Education of the Ministry of Industry in Indonesia in 2018, with a sample of 217 of lecturers. Data collected by using the questionnaire and analyzed by PLS Model with single-mediator. This research reveals that personality and grit have a positive direct effect on the organizational citizenship behavior. The influence of personality on organizational citizenship behavior is partially mediated by job involvement, but job involvement does not mediate the influence of grit on organizational citizenship behavior. Theoritically, the study extends the current theory by exploring grit as an important predictor that influences organizational citizenship behavior and this relationship is not mediated by job involvement.