The present study examines the effect of audit market structure on audit quality and audit pricing. This study is applied in terms of purpose and is causal (post-event) in terms of methodology. The statistical population of the study is companies listed on the Tehran Stock Exchange, and using the systematic exclusion sampling method, 133 companies were selected as the research sample during the 5-year period between 2019 and 2023 (number of observations 665 company-years). The method used to collect information was library and the relevant data for measuring variables were collected from the Kodal site and the companies' financial statements and initial calculations were made in Excel. Then, Stata software was used to test the research hypotheses. The results of the study show that the audit market structure has a direct effect on audit quality according to all three indices of concentration ratio, Herfindahl-Hirschman index, and entropy index. However, the audit market structure concentration ratio index does not affect audit pricing. However, the Herfindahl-Hirschman and audit market structure entropy indices have an inverse effect on audit pricing.