The delay in submitting the auditor's report on financial accounting has attracted the attention of academics and researchers due to the sensitivity of the timeliness of the published information. Timely dissemination of financial accounting information may affect the level of uncertainty in decision making; thus, market behavior is influenced by published accounting information. Audit delays are a major determinant of delays in disclosing financial and accounting information and are a means of monitoring the effectiveness of the audit process. In this regard, researchers have examined the determinants of audit delay in different countries and in different fields. Among the factors that are expected to affect the delay of the audit report are tax avoidance and the size of the auditor. In this study, the effect of tax avoidance on the delay of the audit report has been investigated by considering the adjusting role of the auditor size. The statistical population of this research is the companies listed on the Tehran Stock Exchange and its statistical sample includes data of 105 companies for the 7-year period of 2014-2020. The sampling method was a systematic elimination method. The method used to estimate the model is the multivariate regression method using the combined data method. The results showed that tax avoidance has a positive effect on the delay of the audit report. The results also showed that the size of the auditor reinforces the positive effect of tax avoidance on the delay of the audit report.