Abstract: This study was conducted to determine the effect of whey powder (Lactose: 75%) and Pediococcus Acidilactici bacteria (probiotic) on growth performance and gut improvement of broiler chickens. Day-old male commercial broiler chicks (Arbor Acres) were randomly assigned to treatments. During the experimental period (0-28 days), all chickens were fed the basal diet and different levels of whey powder, Probiotic and whey powder plus Probiotic: (control, W = 1%, P = 0.01%, W+P = 1+0.01% and W+P = 0.5+0.005%). Each diet was offered ad libitum to a group of 40 (4 replication, 10 birds per replication). Throughout the study, body weight, feed intake and Feed Conversion Ratio (FCR) were calculated and at the end of experiment, two birds of each replicate were selected. All birds weighted, then decapitated and viscera were collected immediately, then number of intestinal E. coli, number of cecal oocyste, cecal pH and rate of intestinal lactic acid were detected. Supplementation of whey powder plus Probiotic (1+0.01% and 0.5+0.005%) and whey powder (1%) improved body weight, feed intake and FCR at the end of experimental period (p<0.05). likewise, all treatments except control caused to significant decrease in number of E. coli, number of oocyste and cecal pH (p<0.05). Also the highest and lowest intestinal lactic acid belonged to diet containing whey powder plus Probiotic (1+0.01%) and control, respectively.