The current study aims to provide evidences regarding the audit industry expertise as one of the criteria of auditing quality. For this purpose, in this research the relation between audit industry expertise and auditor's type of opinion is studied using them financial information extracted from listed companies in Tehran Stock Exchange during 2004 - 2012. The previous studies indicated the positive effect of this criterion on quality of auditing in companies. To support the evidences of the former studies, after control of other relevant environmental factors, the results of this study showed that there is a positive and significant relation between audit industry expertise and auditor's qualified opinions. The obtained evidences supported this idea that audit firm specialization could lead to improved quality of financial information of the capital market. Regarding other used variables of the research, the results showed that the auditor size and return of assets negatively, and the company's size and performance of the previous year positively are dependent on the type auditor’s opinion. The results of this study add to the literature of audit quality through study of the role of audit industry expertise as well as the study of the relevant factors to the type of auditor's opinion.

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