This experiment was conducted to investigate the effect of partial substituting diets constituents by Egyptian leek (Allium porrum L.) as unconventional feedstuff in the diets of broiler chickens and its effect on the growth performance, carcass characteristics, and some serum biochemical parameters. A total of 144 unsexed one day old (Cobb 500) broiler chickens were randomly divided into six equal triplicate groups (each replicate contained 8 chicks). A basal control diet was formulated to fulfil the nutrients requirement of broiler chickens according to NRC. In the experimental diets constituents were partially substituted by Egyptian leek (Allium porrum L.) at rate of 2, 4, 6, 8 and 10%. Results revealed that the dietary treatments (4, 6, 8 and 10%) levels of leek had a significant effect (P<0.05) on growth performance parameters than those fed the control diet and other groups. The broilers fed diet contained 8% leek had a significant heavier final body weight, body gain, and best feed conversion ratio as compared to broiler chickens fed other dietary treatments. Percentages weight of liver, heart, stomach and spleen had insignificantly (P>0.05) affected by broilers fed on different levels of leek, while there was a significant (P<0.05) increase in the percentage weight of dressing as compared to those fed control group. Some serum biochemical parameters were significantly (P<0.05) improved due to substitution of the diets constituents with leek as decrease (total cholesterol, triglyceride, low density lipoprotein (LDL) and glucose or increase high density lipoprotein (HDL). It could be concluded that leek could replace up to 8% in broiler diets constituents without any adverse effects on growth parameters, carcass quality and serum biochemical parameters.