An experiment was conducted to study the effects of effective microorganisms (EM) supplementation on broilers performance, immunity and intestinal gross anatomy. Two hundred 1-d-old broiler chicks were randomly assigned to equal five treatment groups A, B, C, D and E. Groups B and C were fed on starter and finisher diets supplemented with 0.4 and 0.6 % EM (Pokashi), while groups D and E were fed starter and finisher diets with the addition of 0.5 ml and 1 ml of Pokashi per liter of drinking water, respectively. Group A was used as control. The EM supplementation improved live body weight and gains during the starter period than those of the control. Feed conversion ratio was not affected during the starter period,  but from 3 to 4 weeks of age, 0.4  and 0.6 % Pokashi supplementation to the diets improved (P<0.05) feed conversion ratio by 13 %  and 15.69 % than the control group. After 42 days of EM supplementation, the absolute or relative values of carcass, gizzard, duodenum, pancreas, liver, small intestine, caecum, heart, head+legs and gastrointestinal tract were not significantly affected. All the nutritional groups reduced significantly (P<0.05) spleen weight index than the control group. Chicks of groups B,C and E had higher antibody titers (P<0.05) against SRBC_S injection after the primary and secondary response than chicks of group A. Chicks in group B showed significant (P<0.05) increase in anti-NDV antibody level than the control. In conclusion, supplementing broiler's diet or drinking water with EM showed some beneficial effects on live body weight ,weight gain and immunity (especially in young growing birds).