ObjectiveTo investigate the role and mechanism of cervical sympathetic ganglia block in alleviation of cerebrovascular spasm (CVS) of rabbits after subarachnoid hemorrhage ( SAH ).Methods A total of 18 healthy male white rabbits whose cervical sympathetic ganglia were successfully blocked were randomly divided into three groups:sham operation group (Group A),SAH group (Group B) and SAH with cervical sympathetic ganglia block group (Group C).Venous blood (2 ml) and cerebrospinal fluid (2 ml) were obtained before the first blood injection ( T1 ),at 30 minutes after injection ( T2 ) and at day 7 after injection ( T3 ),respectively,and conserved in a low temperature refrigerator for spare use.Basilar artery value at T1,T2 and T3 was measured via cerebral angiography.The degree of damage to nervous system at T3 was recorded.ResultsThere was no significant difference in diameter of basilar artery at T1 among three groups.At T2 and T3,the diameters of basilar artery of Groups B and C were shorter than that of Group A,with Group B shorter than Group C,with statistical differences ( P ＜0.01 ).There were no significant differences in NO and NOS in plasma and cerebrospinal fluid at T1 among three groups (P＞0.05).NO and NOS contents at T2 and T3 were lower than those at T1,with Group A lower than Groups B and C,with statistical differences (P＜0.01 ).At T3,the nerve function of Groups B and C were better than that of Group A,with Group C better than Group B ( P ＜0.01 ).Conclusion Cervical sympathetic ganglia block relieves CVS,increases NO content and NOS activity in plasma and cerebrospinal fluid and promotes neural functional recovery after SAH.