To investigate the effects of Clostridium butyricum and Enterococcus faecium on the growth performance, lipid metabolism, and cecal microbiota of broilers, 264 one-day-old male Ross 308 broiler chicks were randomly allocated into four treatments with six replicates in a 2 x 2 factorial arrangement and fed four diets with two levels of C. butyricum (0 or 1 x 10(9) cfu/kg) and two levels of E. faecium (0 or 2 x 10(9) cfu/kg) for 42 days. There was no significant interaction between C. butyricum and E. faecium on the growth performance, lipid metabolism, and cecal microbiota of broilers. However, broilers supplemented with E. faecium had lower (P = 0.022) serum leptin level at day 21 and higher (P < 0.001) fatty acid synthase (FAS), malic enzyme (ME), and acetyl-CoA carboxylase (ACC) mRNA levels in the liver at day 42. Supplementation of C. butyricum improved (P < 0.05) the average daily feed intake and average daily gain, increased (P = 0.016) the serum insulin level at 21 days of age, enhanced (P < 0.05) the content of intramuscular fat, activities of FAS in the liver and lipoprotein lipase (LPL) in the breast muscle, mRNA expression of FAS, ME, and ACC in the liver and LPL in the breast muscle at 42 days of age, but reduced (P = 0.030) cecal Bacteroidetes relative abundance at 21 days of age. The results of this study indicate that the increased intramuscular fat content of broilers fed C. butyricum as observed may be the result of enhanced lipogenesis.