Background and purpose: Animal experiments indicate that the cerebral thrombin is associated with secondary brain damage after intracerebral hemorrhage (ICH). This study was aimed to investigate the concentrations of thrombin-antithrombin complex (TAT) in hematoma fluid and plasma of the patients with ICH after surgery and analyze the correlation between TAT complex levels and severity of ICH. Methods: Sixty patients with ICH were enrolled. Craniotomy for removal of intracranial blood clot was performed within 24 h after ICH. Hematoma fluid and plasma were collected on postoperative days 1, 2, and 4. The plasma obtained from healthy subjects and cerebrospinal fluid from patients without cerebrovascular diseases served as controls, respectively. Enzyme-linked immunosorbent assay was used to determine the concentrations of TAT complex in the patients and controls. Results: TAT complex concentrations in both postoperative plasma and hematoma fluid of patients with ICH were significantly higher than those of the controls (P < 0.01). In patients with ICH, hematoma fluid had a higher TAT complex level than plasma (P < 0.01). The preoperative hemorrhage volume and postoperative TAT complex levels in plasma and hematoma fluid correlated positively with National Institutes of Health stroke scale and negatively with Glasgow coma score (P < 0.01). Conclusion: This study indicates that TAT complex levels of plasma and hematoma fluid correlate positively with the severity of ICH. Determination of the plasma TAT complex concentration is helpful for the evaluation of the severity of post-ICH brain injury.