The present study was carried out to investigate the effect of using graded levels of Avian plus (probiotic) and Natuzyme (enzyme preparation) as feed additives with plant-protein diets on the performance of broiler chicks. Two hundred and fifty two Hubbard broiler chicks were randomly distributed to seven equal experimental groups of three replicates each. At the commencement, the chicks were fed a common starter diet (ME; 3000 kcal/kg and 21.57 % CP) up to 21 days of age; then, they were switched to the experimental grower diets from 22 to 42 days of age. Thus, seven isocaloric (ME of about 3150 kcal/kg)-isonitrogenous (about 19% CP) grower experimental diets were formulated: diet 1 (control), diets 2-4 contained three levels of the probiotic Avian plus (0.05, 0.10 and 0.15% of the diet) and diets 5-7 contained the same three levels of Natuzyme. All chicks were managed similarly and had free access to feed and water during both the starter and grower periods. The criteria of response were live body weight, weight gain, feed intake, feed conversion, economic efficiency of growth, carcass traits, nutrient digestibility [dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), crude fiber (CF) and nitrogen-free extract (NFE), and ash and N retention], and some blood plasma parameters [glucose, cholesterol, total protein, albumin and total lipids, as well as activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in blood plasma]. For the whole experimental period, chicks fed the supplemented diets achieved significantly better means of feed conversion and economic efficiency of growth as compared to the control group. Birds fed the Natuzyme-supplemented diets consumed significantly more feed and exhibited superior final live body weight, weight gain, feed conversion and nutrient digestibility (DM, OM and NFE) as compared to those fed the Avian Plus-supplemented or control diets. Carcass traits and blood parameters of chicks were not significantly affected by dietary treatments. From the previous results, it can be concluded that dietary supplementation with Natuzyme or Avian plus can improve the growth performance of broiler chicks fed plant-protein diets during the growing period, but generally in Natuzyme's favor. Moreover, dietary supplementation with Natuzyme or Avian plus at a level of 0.10% had an advantage over the other two supplementary levels, in view of growth performance and economic efficiency.