Recently, Takata found that a significant level of domoic acid (DA) was detected always in bivalves belonging to a genus Spondylus randomly collected from various tropical areas, and the level of those from the Philippines and Vietnam was considerably high. In the present the study, DA in 25 specimens of S. Vesicolor collected from Nha Phu Bay, Khanh Hoa province, Vietnam was confirmed by HPLC and LC/MS-MS. Distribution of DA in various tissues was also considered. The result showed that the toxicity of the individual sample calculated from these data was 0.99 +/- 0.32 pg/g (n=25) of the whole tissue. These findings indicated that consumption of S. vesicolor from the bay is often not safe from the standpoint of public health. Also, around half of DA(43 percent) was found to be concentrated in the digestive gland, which suggests that origin of DA in S. versicolor was by ingestion of DA-producing species from environment.