Objective: The present study aimed to investigate the expression of COMT mRNA and protein and detect the plasma content of catecholamine (CA), the diameter and thickness of the basilar artery in the early stage of subarachnoid hemorrhage (SAH) to explore the role of COMT in SAH. Methods: SAH was induced by injection of non-heparinized autologous arterial blood into the chiasmatic cistern. RT-PCR and Western blotting were used to detect the mRNA and protein levels of COMT in the rat striatum at different time points (6, 12, 24, 48, and 72 h after SAH). High performance liquid chromatography was performed to detect plasma CA. With HE staining, the basilar artery diameter and its thickness were measured. Results: Compared with the normal group and sham group, the increased expression of mRNA and protein of COMT began at 6 h after SAH(P < 0.01), which peaked at 12 h (P < 0.01); it began to drop 2411 after SAH (P < 0.01). However, 48 h after SAH, the level of COMT (mRNA and protein) was still higher than that of the normal group (P < 0.01). Three days after SAH, the expression of COMT nearly reached normal levels (P > 0.05). For rats undergoing SAH, plasma CA began to increase 6 h after injury, which reached a maximum at 24 h after SAH, and then started to drop. Three days later, it still remained elevated compared with that of the normal group and sham group (P < 0.01). The most marked contraction and increased wall thickness of the basilar artery were found at 24 h after SAH (P < 0.01), which at least lasted for 2 days (P < 0.01), and 72 h after injury, the diameter and thickness of the basilar artery almost reached normal levels (P > 0.05). Conclusion: (1) SAH could induce the expression of COMT in the rat striatum in the early stage. (2) Plasma CA levels were significantly elevated in the early stage of SAH accompanied by cerebrovascular vasospasm (CVS). (3) In the early stage of SAH, increased plasma and CVS may be associated with the insufficient increase and persistence of COMT expression.