Two experiments were designed to investigate the effects of Mn source and concentration on the mRNA expression and enzymatic activities of fatty acid synthase (FAS) and malic enzyme (ME) in cultured primary broiler hepatocytes. In Expt 1, primary broiler hepatocytes were treated with 0 (control), 0·25, 0·50 or 0·75 mmol/l of Mn as inorganic manganese chloride (MnCl2.4H2O) for 24 and 48 h. In Expt 2, primary broiler hepatocytes were incubated with 0 (control), 0·25 or 0·50 mmol/l of Mn as either manganese chloride or Mn–amino acid chelate for 48 h. The mRNA levels and activities of FAS and ME in the hepatocytes were measured in Expts 1 and 2. The results in Expt 1 showed that only at 48 h mRNA expression levels of FAS and ME in the hepatocytes decreased linearly (P<0·001) and quadratically (P<0·02) as supplemental Mn concentrations increased. In Expt 2, compared with the control, Mn supplementation reduced (P<0·01) the activities of FAS, mRNA expression levels of FAS and ME in the hepatocytes, and the efflux of lactic dehydrogenase to the medium. The supplemental Mn at 0·5 mmol/l showed a lower (P<0·03) ME mRNA expression level compared with the Mn group at 0·25 mmol/l. However, Mn source and the interaction between Mn source and concentration had no impacts (P>0·33) on any of the measured cellular parameters. The results suggested that Mn might reduce cell damage and regulate FAS and ME expression at a transcriptional level in primary cultured broiler hepatocytes.