The research was conducted in Ha Long Bay and Cam Ranh Bay, Vietnam from January 2013 to December 2013. Otter clams with and without swollen siphon signs were collected for identification of bacterial species. Bacterial selection media and API 20E tests were used to isolate bacteria species in the study. The result showed there were 7 and 11 bacterial species isolated from otter clam with swollen siphon at the fingerling and commercial stages, respectively. While there were 11 and 6 bacterial species from otter clam without swollen siphon at the fingerling and commercial stages, respectively. However, this study also found 3 bacterial species, including V. a/gino!yticus, V. cholerae and V. splendidus in both otter clam cultured in Ha Long Bay and Cam Ranh Bay. The findings served as baseline information for futher identification of pathogens on swollen siphon disease in otter clam in Viet Nam.