In this research, the effect of corporate governance on choosing audit firms by companies accepted into the Tehran Stock Exchange has been investigated. The sample consisted of 545 observations (year-company) from 2004 to 2008. The audit firm size has been considered an audit quality criterion. The results of testing the research hypotheses by using a logistic regression model by means of the backward elimination method at the levels of all companies show that increasing the percentage of outside directors will increase the possibility of choosing high-quality audit firms. The percentage of institutional ownership (first hypothesis) has a negative meaningful relationship with the possibility of choosing high-quality audit firms as opposed to what was expected. Therefor only the fifth hypothesis of this research has been accepted regarding all companies. After the industry types were separately observed, the industry type was revealed that as a modifying factor it has an important effect on improving the statistics of the model and that it increases the potential of the power of prediction of the presented models.