This study explored the relationship between rumination and job involvement, organizational citizenship behavior, with the mediation of grit. The statistical sample of the research consisted of 300 employees of Iran Oil Pipelines and Telecommunications Company in the Lorestan region, selected through stratified random sampling method. The instruments included mental rumination questionnaire (Nolen-Hooksima et al., 1991), grit questionnaire (Duckworth and Quinn, 2009), job involvement questionnaire (Lodahl & Kejnar, 1965), and organizational citizenship behavior (OCB) questionnaire (Lee and Allen, 2002). Data were analyzed via Structural Equation Modeling (SEM) using SPSS version 26 and AMOS version 22. The proposed model was tested through structural equation modeling. According to the findings, the proposed model was fitted to the data. The results indicated a direct negative effect of rumination along with an indirect effect through grit on both job involvement and organizational citizenship behavior. Based on the findings of the present study, which highlight the importance of grit in enhancing organizational citizenship behavior and job involvement, as well as the negative influence of rumination on organizational outcomes, it is recommended that organizations provide training programs for employees focused on developing grit and managing rumination.