This study aimed to analyze the effect of 'Sintanur' brown rice on Lee's index, fasting blood glucose levels, and HOMA-IR administered to male Sprague Dawley rats. This research was an experimental laboratory study with a post-test-only control group design. The subjects were thirty-five male Sprague Dawley rats divided into five groups. Group 1 consisted of the negative control with a standard diet. Group 2 consisted of the positive control with HFFD-induced obesity for 20 weeks, while groups 3, 4, and 5 were the treatment groups with HFFD-induced obesity for 12 weeks, which were intervened with different dosages of brown rice diet from week 13 to week 20. At week 21, the rats were sacrificed. Fasting blood glucose levels were tested using a glucometer. Fasting serum insulin levels were tested using ELISA. HOMA-IR was calculated using fasting glucose and insulin levels. Serum magnesium levels were tested using Atomic Absorption Spectrophotometry. A non-parametric test of Kruskal-Wallis was used to analyze differences in mean dietary intake, Lee index, fasting blood glucose, and HOMA-IR. As a result, there were significant differences between groups (p<0.05). Spearman correlation test was used to analyze the relationship between the Lee index, fasting blood glucose levels, and HOMA-IR with serum magnesium levels. As a result, there were negative correlations between parameters (r=-0.299; r=-0.393; r=-0.257). Group 5 had the best results in lowering insulin resistance. In conclusion, consuming local 'Sintanur' brown rice decreased the Lee index, fasting blood glucose levels, and HOMA-IR by increasing serum magnesium levels in obese rats. High magnesium intake reduces insulin resistance by correcting the disruption of glucose metabolism and insulin signaling pathways.