OBJECTIVE Insulin resistance is well known to exhibit essential effects on the progression of diabetes mellitus (DM). Guava leaf was also reported to exhibit anti-diabetic effects including decreasing blood glucose. Therefore, this present study aims to explore the role guava leaf extract (GLE) plays in insulin resistance and its mechanism of action via the PI3K/Akt signaling pathway. METHODS KK-Ay mice is a spontaneous genetic type 2 diabetes mouse model induced by feeding a high fat and high sugar diet. Mice were randomly assigned into three groups: diabetic mice (DM), DM + MET (diabetic mice treated with metformin) and DM + GLE (diabetic mice treated with GLE) groups. After 8 weeks of treatment, body weight and levels of fasting plasma glucose (FPG), fasting insulin and lipids in plasma were measured. Mice were sacrificed and mRNA and protein expression of insulin receptor substrate1 (IRS1), phosphatidylinositol 3-kinase (PI3K) and serine/threonine kinase protein B (Akt) in livers were measured. RESULTS GLE markedly reduced body weight, FPG, fasting insulin and insulin resistance index but increased the insulin sensitivity index of diabetic KK-Ay mice. Moreover, GLE upregulated the expression of IRS-1, PI3K and Akt mRNAs in livers of diabetic KK-Ay mice. In addition, GLE also elevated IRS-1, PI3K, Akt, p-PI3K and p-Akt protein expression in their livers. The results of the DM + MET group were similar to those of the DM + GLE group. CONCLUSIONS GLE plays anti-diabetic roles by ameliorating insulin resistance in KK-Ay diabetic mice and this is related to the activation of PI3K/Akt signaling pathway.