Diabetes, is a group of metabolic diseases in which there are high blood glucose levels over a prolonged period. If left untreated, diabetes can cause many complications. The present study was aimed to investigate in vivo, effects of treatment with epicatechin and/or gallic acid efficacy on glycemic state, serum insulin, C-peptide levels, lipid profile and heart function in NA/STZ-induced diabetic rats. The rats were divided into five groups that are normal control, diabetic control, diabetic group treated with epicatechin, diabetic group treated with gallic acid and diabetic group treated with the mixture of epicatechin and gallic acid. The study suggested that treatment of diabetic rats with epicatechin and/or gallic acid markedly improved the impaired oral glucose tolerance, serum insulin level, mRNA expression of GLUT4, insulin resistin, and serum lipid profile and serum enzyme activities related to heart function. Also, the treatment of diabetic group epicatechin and gallic acid together was the most effective in improving the previous indicies.