ERP implementation requires a substantial investment and typically built through project management, which needs a rigorous and in limited time management. ERP implementation requires enormous efforts to implement because it involves all business functions in the organization and partners (ERP vendors and consultants) This paper aims to examine the impact of implementing an enterprise resources planning project on firm performance and organizational citizenship behavior as a moderating variable. The study has surveyed 61 respondents representing 61 manufacturing companies domiciled in the region of East Java, Indonesia, which has adopted an ERP system for more than five years. Survey used questionnaire designed with a five-point Likert scale. The respondent is the key user who is responsible for the success of the ERP system in its business functions of the company. Data analysis used SPSS version 25 to assess the indicator validity and examine the hypothesis developed. The result showed that the implementation of the enterprise resources planning project directly affected firm performance. Second, organizational citizenship behavior directly influences firm performance. Third, the implementation of the ERP project influences firm performance with organizational citizenship behavior as a moderator vari-able. This research provides an insight to project manager in building employee relationship to complete the projects on time. This study also enriches the current research in the supply chain theory.