Background: Hyperglycemia is one of the serious problems that affect humans' lifestyle and require special treatments. Incorrect use of synthetic drugs results in side effects and other problems. Diabetic patients need safer and more effective anti-diabetic drugs that decrease diabetic complications. Natural products are harmless due to conventional medicine can be inefficient (e.g. side effects and ineffective therapy). Objective: Evaluate anti- hyperglycemic activity of aqueous leaves extract of Psidium guajava in hyperglycemic rats. Methods: Adult males albino rats, weighting (140-150 grams) were assigned to one of four groups of six animals each (n= 6). Hyperglycemia induced by single dose intraperitoneal injection of STZ - NA (60 mg/kg - 110 mg/kg, b.wt i.p.), the control groups was given distilled water, the experimental sub-groups were started one week later of STZ induction, then treated once daily by aqueous extract of Psidium guajava leaves until the end of experiment. Initially, blood samples were taken for measured glucose levels and HbA1c. The body weight, urine sugar and blood glucose levels were checked regularly. Results: The polyphenolic of guava leaves extract was found to be (227.63 mg GAE /g. Ex), while flavonoids content was (79.96 mg QE/g. Ex). However, it caused a significant decrease in blood glucose levels and HbA1c and other glycemic indicators. Conclusion: aqueous extract of Psidium guajava leaves possess significant anti-diabetic, and effective in lowering blood glucose level but lack hypoglycemic effect in hyperglycemic rats. Further studies warranted to elucidate possible mechanism(s) of action of the plant material.