Our previous study uncovered potent inhibitory effects of two naphthoquinones from Impatiens balsamina, namely lawsone methyl ether (2-methoxy-1,4-naphthoquinone, LME) and lawsone (2-hydroxy-1,4-naphthoquinone), against α-glucosidase. This gave us the insight to compare the hypoglycemic and hypolipidemic effects of LME and lawsone in high-fat/high-fructose-diet- and nicotinamide-streptozotocin-induced diabetic rats for 28 days. LME and lawsone at the doses of 15, 30, and 45 mg/kg, respectively, produced a substantial and dose-dependent reduction in the levels of fasting blood glucose (FBG), HbA1c, and food/water intake while boosting the insulin levels and body weights of diabetic rats. Additionally, the levels of total cholesterol (TC), triglycerides (TGs), high-density lipoproteins (HDLs), low-density lipoproteins (LDLs), aspartate transaminase (AST), alanine transaminase (ALT), creatinine, and blood urea nitrogen (BUN) in diabetic rats were significantly normalized by LME and lawsone, without affecting the normal rats. LME at a dose of 45 mg/kg exhibited the most potent antihyperglycemic and antihyperlipidemic effects, which were significantly comparable to glibenclamide but higher than those of lawsone. Furthermore, the toxicity evaluation indicated that both naphthoquinones were entirely safe for use in rodent models at doses ≤ 50 mg/kg. Therefore, the remarkable antihyperglycemic and antihyperlipidemic potentials of LME make it a promising option for future drug development.