Abstract: The effect of various levels of microbial culture (EM4) on nutrient digestibility and performance was studied in 120 male broilers. The birds using water supplemented with EM4 gained more weight and used their feed more efficiently than those of control group. However, feed consumption remained unaffected. The highest weight gain and the best feed efficiency was observed in the broilers using the lowest amount of EM4 in the water. The mean values being 1370, 1524, 1563 and 1569 g for weight gain and 3.0, 2.68, 2.65, and 2.55 for feed efficiency (g feed/g gain ) in groups A, B, C and D, respectively. Use of EM4 did not show any effect on dressing percentage and on the relative weight ( g/100g body weight ) of liver, heart, pancreas and gizzard indicating no anatomical changes in the internal organs. Digestibility of dry matter, crude protein and crude fibre contents of the rations also remained unaffected.