Objective:To investigate the relationship between body mass index (BMI) and gestational hypertension using two-sample Mendelian randomization analysis.Methods:The summary level data for BMI and gestational hypertension were obtained from the genome-wide association study (the deadline for data inclusion was October 31, 2023). All data were analyzed by inverse variance weighting, MR-Egger regression, weighted median, simple model and weighted model methods. Cochrane Q test was used to evaluate heterogeneity, MR-Egger regression intercept test and funnel plot were used to assess horizontal pleiotropy. Results:Inverse variance weighting result under fixed effects and random effects models showed that the risk of gestational hypertension increased with the increase of BMI ( OR = 1.62 and 1.62, 95% CI 1.39 to 1.88 and 1.39 to 1.88, P<0.01). Sensitivity analysis results including MR-Egger regression, weighted median and weighted model methods showed that BMI increased the risk of gestational hypertension ( OR = 1.51, 1.56 and 1.71; 95% CI 1.01 to 2.26, 1.23 to 1.99 and 1.09 to 2.69; P<0.05 or <0.01). Although Cochrane Q test result showed evidence of heterogeneity ( P = 0.04), inverse variance weighting under a random model suggested that BMI increased the risk of gestational hypertension. Horizontal pleiotropy was not observed in the above analysis ( P = 0.73). Conclusions:Obesity may increase the risk of gestational hypertension. Pregnant women should pay attention to weight control to decrease the risk of gestational hypertension.