This research aims to study agency costs and tax planning, emphasizing the moderating role of government ownership. Taxation, as the primary means of raising revenue, can help governments achieve their macroeconomic objectives. Paying taxes is one of the most important tasks citizens can perform to provide financial resources for social welfare. In addition, politically connected companies have an opaque operating environment due to government support, resulting in more significant conflicts of interest and higher agency costs. To achieve this purpose, two hypotheses were formulated. To test these hypotheses, a sample of 142 companies was selected from the companies listed in the Tehran Stock Exchange during 2014-2023. A multivariate regression model was applied using the panel data method. The results of the research hypotheses indicate that agency costs and tax planning have a positive and significant relationship. The results also suggest that government ownership does not affect the relationship between agency costs and tax planning.