The efficacy and mechanism of flaxseed lignan secoisolariciresinol diglucoside (SDG) on glucose hemostasis in obese mice were examined. Male C57BL/6J mice fed on a high-fat diet (60 kcal% fat) for 15 weeks were divided into four groups and treated by oral gavage with 0, 10, 100, or 1000 mg/kg/d of SDG dissolved in water for 6 weeks. Age-matched mice fed with a low-fat diet (10% kcal fat) were used as the normal control. SDG lowered fasting blood glucose, insulin, and free fatty acid levels and improved oral glucose tolerance, insulin response, and homeostatic model assessment-estimated insulin resistance index in mice fed the high-fat diet. Flaxseed SDG also increased GLUT4 expression and tended to increase phosphorylated AKT to total AKT ratio in the muscle tissue. The data demonstrated that flaxseed SDG improved glycaemic control, at least in part, by enhancing insulin signalling and sensitivity in diet-induced obese mice.