To evaluate the potential beneficial impact and to clarify the underlying mechanisms of triiodothyronine (T3) on glucose intolerance in aged rats. Rats were divided into adult group, aged group, and T3-treated aged group (T3-aged). T3 was administered at a dose of 8 µg/kg body weight for 2 weeks. In comparison to adult group, aged rats presented significant higher levels of fasting insulin and homeostatic model assessment of insulin resistance (HOMA-IR). Glucose area under the curve (AUC), and peak glycemia, estimated from oral glucose tolerance curve, were significantly increased along with decreased mRNA expression of skeletal muscle sirtuin-1, glucose transporter-4 (GLUT-4) and uncoupling protein-3 (UCP-3) in aged versus adult group. T3 administration significantly decreased the serum levels of fasting insulin, HOMA-IR, glucose AUC, and peak glycemia in T3-aged versus aged rats. Skeletal muscle mRNA expression of sirtuin-1 and GLUT-4 were increased, whereas UCP-3 was not changed by T3 administration. T3 administration improved glucose intolerance, and decreased insulin resistance in aged rats. This was associated with upregulation of skeletal muscle sirtuin-1 and GLUT-4 which could mediate such beneficial effect.