Accurate assessment of systematic risks in financial markets can lead to favorable capital allocation. Systematic tail risk is adverse events that, if they occur, can affect stock returns. Therefore, the purpose of this study is to investigate the effect of tail risk on excess stock returns. In the present study, two criteria of cumulative tail risk and combined tail covariance risk were used to measure tail risk. For this purpose, using the systematic removal method, a sample of 136 companies listed on the Tehran Stock Exchange (TSE) in the period 2009 to 2019 was selected. Research hypotheses were tested using the five-factor model of Fama and French regression. The results showed that the combination of size portfolio and tail risk and the combination of value portfolio and tail risk have a negative effect on excess stock returns. In addition, the results indicate that the combination of profitability portfolio and tail risk and the combination of investment portfolio and tail risk does not lead to excess stock returns. In general, the results showed that tail risk can be added to asset pricing models in addition to the variables of the five-factor model of Fama and French.