Abnormality of thyroid hormones in liver diseases is common, but data is lacking in patients with type A hepatic encephalopathy (HE). The present study was aimed to determine whether there was an abnormality in thyroid hormones among patients with type A HE. We measured the levels of thyroid hormones in 36 acute liver failure (ALF) patients with type A HE and in 29 acute liver injury patients (international normalized ratio, INR = 1.5) without encephalopathy as control. The clinical parameters associated with abnormality of thyroid hormones were evaluated. ALF patients with type A HE exhibited decreased TSH levels compared to patients without encephalopathy (0.17 vs 1.08 mu IU/mL, P < 0.001). There was no difference in T3 and T4 levels (both total and free) between the two groups. The logistic regression analysis identified type A HE as an independent related factor for the occurrence of low TSH (Odds Ratio = 12.32) in patients with ALF. Correlation analysis showed that there was an inverse correlation between TSH level and the grade of encephalopathy (r = -0.795). Furthermore, patients with low TSH depicted poor survival rate than those with normal TSH level (29.3% vs 44.1%, P = 0.003). Patients with type A HE exhibited subclinical central hypothyroidism, and had significant decreased TSH level, which had inverse correlation with the grade of encephalopathy. The reduced TSH was associated with poor survival rate.