The degree of hepatopathy affecting the synthesis of α2-macroglobulin (α2M) as an acute phase protein in rats was investigated. Hepatopathy was induced in Sprague-Dawley rats by intravenous administration of galactosamine at a dose of 30 mg/kg for 7 days. Inflammation was induced by intramuscular injection of turpentine oil at a dose of 2 mL/kg. Blood was collected before turpentine oil injection and at 24, 48, 72 and 96 h after injection. Serum concentrations of α2M were measured by enzyme-linked immunosorbent assay. Mean values of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in rats administered galactosamine were significantly higher than in controls. Mean values of body weight and total protein were significantly lower than in controls. Serum concentrations of α2M in the galactosamine group were significantly lower than in controls. Kinetic parameters, area under the concentration-time curve (AUC0–96) and maximum serum concentration (Cmax), were significantly lower than in controls. The cut-off value for detecting the effects on synthesis of α2M in liver was 46.9 mg·h/mL. Seven rats (77.8%) were assessed for decreases in the synthesis of α2M due to hepatopathy. Two rats showed no influence on the synthesis of α2M, despite administration of galactosamine. AST and ALT in these two rats were ≤ 285 and ≤ 174 U/L, respectively. In conclusion, synthesis of α2M in rats is evidently suppressed in the severe stages of hepatopathy.