This study investigated the effects of dietary supplementation with the effective microorganism (EM) on the growth performance, blood parameter, small intestinal microflora, and noxious gas emission of broilers. A total 720 1-d old ROSS 308 was randomly assigned to 6 dietary treatment groups: control, virginiamycin (6 mg/kg), 0.1% PB 0.1% EM, 0.5% EM, and 1.0% EM. Each treatment was fed to 4 replicates of 30 birds per diet for d 35. Two-phase feeding program with a starter diet from 0 to 3 wk, and a finisher diet from 4 to 5 wk was used in the experiment. Within each phase, a diet was formulated to meet or exceed NRC requirements of broilers for macro-and micronutrients. The diet and water were available ad libitum. Result indicated that during overall periods of the experiment, final weight, body weight gain, and feed intake were not different among dietary treatments. Feed conversion ratio was less (P<0.05) for EM treatments than control, antibiotics, and PB. Total cholesterol (TC), triglyceride (TRG), glucose (GLU), total protein (TP), calcium (CA), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were not different among dietary treatments. White blood cell (WBC), hemoglobin (Hb), heterophils (HE), lymphocyte (LY), monocytes (MO), and eosinophils (EO) were not different among dietary treatments. HE:LY was less (P<0.05) for EM0.5 treatments than control, antibiotics, and PB. Lactobacillus was greater (P<0.05) for EM treatments than control and antibiotics. E. coli and Salmonella were not different among dietary treatments. NH 3 and CO 2 wereless (P<0.05) for EM treatments than control. These results indicated that EM treatments were effective feed conversion ratio, noxious gas emission and micro flora population on the cecum in broilers.