Service outsourcing is a strategy that has recently been used to create the ground for the optimal use of the expertise of the organization’s staff. The purpose of this study is to investigate the relationship between outsourcing activities of Isfahan province’s bureau of taxation affairs and their organizational performance. The research method is applied in terms of purpose and terms of nature, and the method is descriptive-correlation with the survey method. For this purpose, a sample of 349 subjects was selected among 3750 employees of Isfahan province’s bureau of taxation affairs by the multi-stage cluster sampling method. To collect data, the organizational performance questionnaire and outsourcing questionnaire were used and to assess the validity and reliability of the questionnaire, content validity and Cronbach’s alpha method was used, respectively. With applying structural equation modelling, Lisrel software was used to analyze the data and test the hypotheses. The results of the study revealed that there is a significant relationship between the outsourcing of the Isfahan province’s bureau of taxation affairs and their organizational performance. Accordingly, outsourcing activities have a significant relationship with fast-track activities, increasing the quality of services, using employee expertise, increasing customer satisfaction and reducing organizational costs. The feedback on the results of this research helps the Isfahan province’s bureau of taxation affairs to eliminate the shortcomings of outsourcing activities. Second, the use of the effects and consequences of outsourcing activities effectively improves organizational performance through its relationship with increasing the quality of services, reducing organizational costs, fast-track activities, upgrading customer satisfaction, and increasing the specialized skills of employees using employees’ expertise.