Abstarct: Investment decisions in financial markets are influenced by behavioral and psychological factors, in addition to economic and informational variables. Research conducted in the field of behavioral finance shows that these factors can lead to deviations in investors' judgments; however, the intensity and significance of the effect of behavioral biases have not been reported equally in different studies. Therefore, conducting a comprehensive study seems necessary to consolidate and compare the results of previous research. In this study, using the mexta-analysis method, the results of domestic and foreign studies related to behavioral biases affecting investment decisions have been examined. After identifying and screening eligible studies, data related to behavioral biases were extracted and analyzed separately for each bias in CMA v3 software. In order to evaluate the differences between the results of the studies, heterogeneity tests were performed and an appropriate statistical model was selected for analysis. The findings of the study showed that there is significant heterogeneity among the studies reviewed; accordingly, the analyses were conducted using a random effects model. The results of the mexta-analysis indicate that a significant portion of the behavioral biases reviewed have a significant impact on investment decisions, while for a number of other biases, no significant effect was observed. Also, the comparison of the effect sizes of the significant biases showed that herd behavior has the largest effect size among the biases reviewed.