Background: Obesity typically results from a variety of causes and factors which contribute, genetics included, and style of living choices, and described as excessive body fat accumulation of body fat lead to excessive body, is a chronic disorder that combines pathogenic environmental and genetic factors. So, the current study objective was to investigate the of the FTO gene rs9939609 polymorphism and the obesity risk. Explaining the relationship between fat mass and obesity-associated gene (FTO) rs9939609 polymorphism and obesity in adults. Methods: Identify research exploring the association between the obesity risk and the variation polymorphisms of FTO gene rs9939609. We combined the modified odds ratios (OR) as total groups and subgroups. A stable and random effect processes with standard mean division was used to evaluate the outcomes of this study in dominant and recessive groups. The purpose of the current meta-analysis was to explain the relationship of FTO rs9939609 and obesity. Results: This meta-analysis comprised 8 eligible studies including 4109 participants, comprising of 2441 cases and 1668 control measures. Meta-analysis outcomes exposed that a significant difference (P < 0.05) of the FTO genotypes appeared between the obese and the control groups. The FTO rs9939609 polymorphisms were associated significantly with the increased risk of obesity in five genotypes of adults: the AA + AT vs. TT genotypes, OR = 1.54, 95% CI = 1.34–1.77, p = 0.00001; the AA vs. AT + TT genotypes, OR = 1.40, 95% CI = 1.16–1.69, p = 0.0004; the AA vs. TT genotypes, OR = 1.79, 95% CI = 1.45–2.21, p = 0.00001; the AT vs. TT genotypes, OR = 1.47, 95% CI = 1.26–1.72, p = 0.00001; and the A vs. T alleles, OR = 1.38, 95% CI = 1.26–1.53, p = 0.00001). Conclusion: This meta-analysis reveals that the FTO gene polymorphism rs9939609 is correlated with the increasing obesity risk and A allele is also considered as a risk factor for the obesity susceptibility.