The aims of this study are to investigate the feasibility and validity of the L-[1-¹³C] phenylalanine breath test (¹³C-PheBT) which has been used to measure hepatocyte functional capacity in hepatitis B virus-related liver disease patients and to propose validity parameters of the test in 12 healthy volunteer, 8 chronic hepatitis and 26 liver cirrhotic patients. 100mg/body nonradiative L-[1-¹³C] phenylalanine (¹³C-Phe) was administered orally to all subjects. Breath samples were taken before and different intervals within 360 min after administration. The ¹³CO₂/¹²CO₂ enrichment was assessed by isotope ratio mass spectrometer. The parameter percentage ¹³C excretion rate ¹³CER_t (% ¹³C dose/h) all peaked within 10-30 min after oral ¹³C-Phe application. The parameters such as maximum value of ¹³C excretion rate, ¹³CER_max (% ¹³C dose/h) (controls: 18.0±3.3; Child A: 11.0±3.8; Child B: 5.0±0.5; Child C: 3.6±1.2), ¹³C excretion rate at 30min, ¹³CER₃₀ (% dose/h) (controls: 11. 9±2.1; Child A: 8.1±0.4; Child B: 6.1±0.9; Child C: 3.2±1.2), ¹³C cumulative excretion of first 60 min, ¹³Ccum₆₀ (% ¹³C dose) (controls: 9.3±1.4; Child A: 6.6±0.7; Child B: 4.1±0.3; Child C: 2.6±0.9) and half time of ¹³C excretion rate, T_1/2 (minutes) (controls: 40.4±4.4; chronic hepatitis: 53.4±4.4; Child A: 59.8±4.5; Child B: 102.0±17.3; Child C: 212.1±87.9) were effective indexes which could be employed to stage hepatocyte impairment and liver functional reserve of advanced HBV-related cirrhotic patients (i.e. healthy subjects, Child A, B, C); T_1/2 was also useful for distinguishing mild HBV-related liver injure.