1,3,5-Trinitro-2-acetyl pyrrole (TNAP) is a product derived from the reaction of 2-acetyl pyrrole with nitrite in the model of Maillard browning systems. This compound is moderately mutagenic to the Salmonella strains TA98 and TA100 and is markedly cytotoxic to mouse C3H10T1/2 cells. Experiments are performed to investigate the effects of TNAP on the hepatic toxicity in mouse. Male BALB/C mice were subjected to a dose of 7.2 mg/kg body weight twice a week by i.p. injection for 24 weeks, then followed by a feeding diet for 21 weeks. TNAP-treated mice showed an increase in mortality and time-dependent appearance of lesions in the liver. TNAP is hepatotoxic as demonstrated by a marked increase in the activities of serum alanine transaminase (ALT) and aspartic transaminase (AST). TNAP-related lesions observed histologically in mice, included hapatic atrophy, mild fatty metamorphosis with multilocular cysts in the liver. In conclusion, TNAP was considered to be a toxic compound in mice as evidenced by increased incidences of mortality, and lesions of liver.