Corporate investment decisions are determined by a variety of factors, including various managerial measures, including overconfidence of managers, which are important determinants of corporate investment decisions. Most corporate executives prefer internal financing, but if internal resources are not sufficient to meet this need, they use external resources with the least degree of information asymmetry. The purpose of this study was to investigate the effect of managerial overconfidence on investment and the moderating effect of the internal financing method is on their relationship. The study consisted of listed companies in Tehran Stock Exchange during the period 2011 to 2016 and using a systematic elimination sampling method, 97 companies were selected. To investigate the research hypotheses, EVIEWS software and panel data regression method was used. The results of the research showed that managers’ overconfidence has a positive and significant effect on investment as well as underinvestment, but internal financing does not have a significant effect on the relationship between the overconfidence of managers and investment as well over-investment. But the effect of internal financing on the relationship between managers’ overconfidence and underinvestment was a significant positive. Finally, it became clear that internal financing had a significant negative impact on investment and over-investment.
