According to audit standards, internal controls affect the auditor’s reliance on collected auditing evidence and the process of determining the type, nature, and timing of engagement and the range of audit methods. This research aims at exploring the effects of internal controls quality on audit report lag on the firms enlisted in Tehran Stock Exchange. To this end, the research data for the period after the enactment of internal controls instructions, during the years from 2012 to 2015 were analyzed. The results indicate a significant, positive relationship between internal control weaknesses and audit report lag. In other words, not weakness in internal controls is associated with punctual audit report. The research findings provide empirical evidence regarding the common viewpoint in audit standards, based on which internal controls affect the process of determining the timing of audit engagement.