It is well documented that N-acetyltransferase (NAT) plays a key role in the N-acetylation of arylamine compounds. Ellagic acid was demonstrated to elicit dosedependent bacteriostatic activity and inhibition of N-acetylation of 2-aminofluorene (AF). N-acetylation of AF in S. aureus was determined by high preformance liquid chromatography. The apparent values of Km and Vmax of NAT were decreased after co-treatment with 0.5 mM ellagic acid in the cytosol of S. aureus. PCR also indicated that ellagic acid inhibited NAT gene expression (NAT mRNA) in S. aureus.