The present study investigates the effect of managers' short-sightedness on abnormal stock returns with an emphasis on institutional investors. This research is applied in terms of purpose and in terms of methodology of correlation is causal (post-event). The statistical population of the study was the companies listed on the Tehran Stock Exchange and using the systematic elimination sampling method, 129 companies were selected as a sample of the research in an 8-year period between 1392 and 1399. The method used to collect information is a library and the relevant data for measuring variables were collected from Kedal website and companies' financial statements and in Excel preliminary calculations were performed and then Stata software was used to test the research hypotheses. The results of the study show that managers' short-sightedness has a direct effect on abnormal stock returns. However, institutional investors have the opposite effect on the relationship between managers' short-sightedness and abnormal stock returns.