Background: The objective is to investigate whether the 13C-phenylalanine breath test(PBT) would be useful for the evaluation of hepatic function in patients with chronic hepatitis B, liver cirrhosis and minimal hepatic encephalopathy (MHE). Methods: L- [1-13C] phenylalanine was administered orally in a dose of 100 mg to 80 patients with liver cirrhosis, 20 with chronic hepatitis B and 20 healthy subjects. The PBT was measured at 8 different time points (0, 10, 20, 30, 45, 60, 90, 120 min) to obtain the values of Delta over baseline, percentage 13CO2 exhalation rate and cumulative excretion (Cum). The relationships of the cumulative excretion with the 13C-%dose/h and blood biochemical parameters were investigated. Results: The 13C dose h -1 at 20 and 30 min combined with the cumulative excretion at 60 and 120 min showed correlations with the chronic liver diseases, especially Child-Pugh score and MHE or not. And the data showed correlations with serum albumin hemoglobin platelet and Child-Pugh score. Prothrombin time, total and direct bilirubin were significantly increased, while serum albumin, hemoglobin and platelet, the cumulative excretion at 60 and 120 min values decreased by degrees in healthy controls, Child-Pugh A, B, and C patients (P<0.01). Similar results of PBT were in the patients with and without MHE, while only prothrombin time prolonged and total bilirubin increased (P<0.05). Conclusions: The PBT can be used as a non-invasive assay to evaluate hepatic function in patients with liver cirrhosis and MHE. The %13C dose h-1 at 20 min, %13C dose h-1 at 30 min and cumulative excretion at 60 min may be the key value for determination at a single time-point.