OBJECTIVE To analyze the relationship between hepatorenal syndrome (HRS) and plasma ammonia. METHODS Plasma ammonia, liver and renal function of 465 patients with liver cirrhosis in our hospital, from June 2007 to March 2009, were analyzed. 80 renal dysfunction patients and 80 healthy controls were recruited in the control group. In addition, 40 patients with HRS were followed up. RESULTS Using urea as the diagnosis standard of HRS, the morbidity rate of HRS was 39.6%, which was higher than that using creatinine as the diagnosis standard of HRS (Chi-square test = 97.33, P less than 0.01). using urea and creatinine as the diagnosis standard of HRS, the ammonia level of HRS groups was (57.39+/-48.83)mumol/L, (64.80+/-47.25)mumol/L, which were higher than that in the non-HRS groups (t = -3.07, t = -3.67, P less than 0.01). The ammonia level of patients with renal dysfunction was (26.59+/-14.34)mumol/L, which was lower than that in HRS group, non-HRS group (P less than 0.01), but there was no statistical significance between the patients with renal dysfunction and the healthy peoples [(22.36+/-8.72)mumol/L] (t = 1.52, P more than 0.05). The followed-up analysis of 40 patients with HRS indicated that plasma ammonia level was positively correlated with urea and creatinine, and correlation coefficients were 0.874 and 0.834 (P less than 0.05). CONCLUSIONS Hepatic encephalopathy is liver-kidney-intestine-brain syndrome. HRS plays an important role in the development of hepatic encephalopathy.