The present experiment was conducted with Hubbard broiler-type chicks in a factorial arrangement of treatments (3×2) to investigate the effects of feeding diets fortified with three levels of sunflower oil on growth performance of broiler chicks kept at two stocking densities during summer season. Three isonitrogenous experimental diets, fortified with sunflower oil (0.00, 1.25 or 2.50% of the diet), were formulated and used. The chicks were kept in battery cages at two stocking densities (9.04 and 11.3 birds/m²). All chicks were fed their respective experimental diets and had free access to feed and water throughout the experimental period from 2 to 6 weeks of age. The criteria of response were growth performance, nutrient digestibility, carcass traits and some blood parameters.                 The obtained results can be summarized as follows: Apart from the effect of cage density,  dietary supplementation with sunflower oil level increased significantly the growth performance of broiler chicks (final body weight, body weight gain and feed conversion), nutrient digestibility of diets (dry matter, organic matter, crude protein, ether extract and nitrogen retention), and blood plasma glucose concentration. However, dietary oil supplementation did not affect feed intake, carcass traits, digestibility of crude fiber and nitrogen free extract or ash retention as well as blood plasma concentrations of cholesterol, total protein, albumin, globulin, triglycerides, or activity of  AST and ALT. Decreasing stocking density led to significant  increases in final body weight, body weight gain, feed conversion, and digestibility of dry matter, organic matter, crude protein, nitrogen free extract and nitrogen retention, and in plasma triglycerides concentration. However, stocking density did not affect feed intake, carcass traits, digestibility of ether extract, crude fiber and ash retention and blood plasma concentrations of glucose, cholesterol, total protein, albumin and globulin or activity of AST and ALT. The effect of interaction between dietary sunflower oil and cage density was not significant for most variables examined in the present study. Based on the results of this study, it can be concluded that reducing stocking density and dietary supplementation with sunflower oil in summer season can be used for obtaining normal growth performance of broiler chicks.