This study was conducted to investigate in vivo antimicrobial potential of garlic against Clostridium perferinges and resultant promotant effects on performance of the broiler chickens. Garlic powder was used as an alternative to GPAs (Growth Promotant Antibiotics) to prevent subclinical Necrotic Enteritis (NE) due to C. perferinges. 120 day-old broiler chicks were randomly distributed to six treatment groups of 20 chicks each (2 replicates(-10) chicks). Six isonutrient diets supplemented with garlic at graded levels of 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 g kg(-1) were fed to the birds for seven weeks. Data were collected weekly on performance parameters including feed intake, weight gain and feed conversion ratio (FCR). Also, on the 21 35 and 49th days of the study, two birds per group were randomly selected, slaughtered and dissected. 1 g of caecal contents per each bird were sampled into labelled sterile sample bottles. The samples were subjected to culturing, bacterial identification and colony counting. All data were subjected to analysis of variance. Results showed that garlic significantly (p > 0.05) depressed feed intake (3310 g feed/bird at 1.0 g kg(-1) supplementation) but improved FCR. The supplement has no significant effect on weight gain but C. perfringens colony counts in the treated groups, were numerically reduced (lowest count, 0.93 x 10(5) cfu g(-1) at 1.0 g kg(-1) supplementation), as compared to the control. It is therefore concluded that diets could be supplemented with garlic at dose range of 1.0 to 1.5 g kg(-1) to prevent subclinical NE and achieve improved performance in birds.