This study examines how important human resources are for gaining competitive advantages in businesses that are hard for competitors to copy. It suggests that both private and public organizations should closely examine and take action on policies and strategies related to employee performance behaviors at work. The focus of the research was to understand the role of organizational citizenship behavior (OCB) as a middle step between organizational culture (OC) and the performance of employees in their assigned roles (In-role performance or IP). To collect data, online surveys were sent to employees in Thailand, which were designed based on previous research and checked for reliability using the Cronbach alpha coefficient. The study received 211 responses, which was a satisfactory number based on calculations from the G*Power program and analysis using partial least squares structural equation modeling (PLS-SEM). The findings showed that OC positively affects all aspects of OCB, including civic virtue (CV), conscientiousness, courtesy (CY), altruism (AL), and sportsmanship (SP), with CY and CV having a positive impact on IP. OC was found to indirectly influence IP through two aspects of OCB, CY, and CV, with statistical significance. Structural equation modeling showed that these relationships could explain up to 79.1% of the variation in IP. The study concludes that by fostering a culture that promotes CV and CY, organizations can enhance their competitive and cultural advantages through improved employee performance.