The present study was designed to investigate the chemical composition of guava (Psidium guajava) and mango (Mangifera indica) leaves and evaluate their potential effect as hpolipidemic agents in experimental animals. Twenty five male albino rats were divided into five groups (group A, represent control; group B, was received high fat diet to serve as positive control, group C, feeding on diet contain 10% mango leaves, group D, feeding on diet contain 10% guava leaves and group E, feeding on diet contain 5% guava and 5% mango leaves. Proximate analysis of guava and mango leaves showed that they contain: total carbohydrates (70.66% and 75.53%, respectively), crude protein (22.78% and 18.45%, respectively), ash (5.47% and 4.82%, respectively) and crude fat (1.09% and 1.2%, respectively). Total phenolic compounds in guava and mango leaves were 118.1 and 73.7 mg/g, respectively, while, total flavonoids were 11 and 9.75 mg/g, respectively. Fourteen phenolic compounds were identified from the results of the HPLC analysis of the methanolic extract of leaves of both guava and mango. The most important compounds in guava leaf extract were gallic acid, catechin, and chlorogenic acid, while catechin, Pyro catechol, and gallic acid were the most important compounds in the alcoholic extract of mango leaves.  The most important results of the biological experiment indicated that group B was the worst of all measures of levels of bad fats in the blood (triglycerides, total cholesterol and LDL-cholesterol). Both guava and mango leaves (groups C and D) led to a significant decrease in the levels of triglycerides, total cholesterol and LDL-cholesterol, while group E (mix of guava and mango leaves) showed the best results in general. In a conclusion, both guava and mango leaves can be used in diets to lower blood fats.