<i>Background:</i> Serine protease inhibitor member 3 of clade A (SERPINA3), also known as alpha-1-antichymotrypsin, inhibits the activity of cathepsin G. The release of neutrophil cathepsin G (proteolytic enzyme) can destroy the vascular matrix through degradation, platelet aggregation and coagulation disorders. In a previous report there was evidence that an alanine/threonine polymorphism was associated with the risk factor for aneurysmal subarachnoid hemorrhage (SAH) in a Polish population. We performed this study to determine whether this A15T polymorphism shows the same association in a Japanese population. <i>Methods:</i> A total of 437 patients with an aneurysmal SAH and 405 control cases of Japanese origin were genotyped for the A15T polymorphism and 2 further intronic single nucleotide polymorphisms by using polymerase chain reaction and direct sequencing. <i>Results:</i> In the patients with intracranial aneurysms the SERPINA3 A15T allele and genotype distribution did not differ significantly from the controls. <i>Conclusion: </i>In the Japanese population the A15T polymorphism of the SERPINA3 gene is not associated with aneurysmal SAH.