This study was carried out to evaluate the effect of onion and garlic in experimentally induced diabetic rats by meta-analysis of related studies. Ten systematic literature searches were conducted on the National Center for Biotechnology Information database, the DBpia database, and the Koreanstudies Information Service System database. Most studies had three groups-the normal group, the treated diabetic group, and the untreated diabetic group-the means of which were compared for various effect factors between two of the groups. The effect factors were blood glucose concentration, body weight, and the concentrations of plasma total cholesterol, plasma triglycerides, plasma high-density lipoprotein-cholesterol, and liver glycogen. The treated diabetic group included diabetic rats supplemented with either onion or garlic extract or with single components, including S-allylcysteine sulfoxide, S-methylcysteine sulfoxide, and diallyl trisulfide. The effects of each factor were investigated by the standardized mean difference between the treated diabetic group and the diabetic group. Because homogeneity among studies for some effect factors is not plausible, the random effect estimates were calculated. In the meta-analysis, the antidiabetic effects of onion extract and single components were significant for glucose concentration and body weight (P < .05), but the effects of garlic extract were not significant. The results of the meta-analysis suggested that the single component intake and onion extract intake may be effective for lowering plasma glucose concentrations and body weight.