The present study attempts to merge studies and their conclusions on the relationship between religion and happiness using meta-analysis and systematic review methods. Therefore, the articles published in scientific research journals and university theses related to the subject of the study that met other inclusion criteria were identified and included in the analysis. After screening 54 works, and applying exclusion criteria, 14 studies were included in the final analysis. The findings showed the heterogeneity of the effect size and lack of publication bias in the studied studies. Then, the random effect size coefficient was evaluated using the second edition of the CMA software, considering the heterogeneity of the studies and the mediating role of the four variables. According to the findings the size of the combined effect for the relationship between religion and happiness is 0.311, which is considered average according to Cohen's interpretation system. Also, "the time frame of research ", " the place of study", "statistical population", "researchers' field of study ", were mediating variables and the effect size coefficient for their classes was calculated as follows: for studies before and after 2016, it was 0.455 and 0.342, respectively. Also, the coefficient of combined effect was 0.415 for studies conducted in the central regions of Iran and 0.315 for other regions. Also, the combined effect size coefficient of studies in the field of sociology was lower than other fields. This difference is consistent with the theoretical expectations. The results suggested that religion, has a distinct effect on happiness by moderating the above four variables. Finally, driven by the results of this study, some strategies are presented to improve this relationship.