Abstract: The present research was conducted on Hubbard Isa Starbro broilers to evaluate the dynamics of probiotics relating to balanced growth of intestinal flora and histological reactions and changes within the crop and cecal tissues. A total of eighty day-old broiler chicks were divided into four groups of equal numbers as group A (Probiotics fed group vaccinated), B (Probiotics fed group nonvaccinated), C (Conventional fed group vaccinated) and D (Conventional fed group nonvaccinated). Group C and D were taken as control birds fed with commercial ration and groups A and B as experimental birds were fed with commercial ration with the addition of 2 g probiotics (Protexin® Boost)/10 L drinking water upto 6th week of age. The effect of probiotics with regard to clearing bacterial infections and regulating intestinal flora was evaluated by determining the TVC and TLC of the crop and cecum samples of probiotics and conventional fed groups at the 2nd, 4th and 6th week of age. The result revealed competitive antagonism. The result of the study evidenced that probiotic organisms inhibited some nonbeneficial pathogens by occupying intestinal wall space. It has been demonstrated that broilers fed with probiotics had a tendency to display pronounced intestinal histological changes such as active impetus in cell mitosis and increased nuclear size of cells, than the controls. It is obviously found from this research work that probiotics supplementation promoted significant influence on intestinal microbial balance related with pronounced intestinal histological changes.