Abstract: Twelve healthy controls, eight patients with chronic hepatitis graded G2S2,twelve patients with compensated liver cirrhosis, twelve patients with decompensated liver cirrhosis are studied by L-1-13C-phenylalanine breath test which is longed for 6 hours and 24 breath samples per subject are collected. 13CO2 enrichment are measured by isotope ratio mass spectrometer. The results show that 13CO2 half excretion time T1/2 can significantly differentiate the four groups(P<0.05), however the 13CER30 and 13Ccum6o can differentiate normal subjects, patients with compensated liver cirrhosis and decompensated liver cirrhosis, but the discrepancy of the them are not significant between patients with chronic hepatitis and healthy controls or patients with compensated (P>0.05). The three parameters are significantly correlated with some standard clinical serum-biochemical datum(P<0. 05), but not the level of serum alanine transaminase(AL)and aspartate transaminase(AST). So,L-1-13C-phenylalanine breath test may be a promising clinical tool to grade chronic liver disease, which is safe, simple, quantificational and effective.