Abstract: Vibrios are halophilic bacteria and are ubiquitous in marine environments. The diversity of these bacteria in tropical areas is not clearly understood. In this study, Vibrio spp. including Vibrio parahaemolyticus were investigated at the Andaman Tarutao Island, Thailand. Water samples were collected at Son Bay and Ruesri Bay located on opposite sides of the island. The total numbers and the predominance of Vibrio spp. were determined by cultivation on thiosulfate citrate bile- salts sucrose agar. Enumeration of V. parahaemolyticus was performed on CHROMagar Vibrio. There was no correlation between the total numbers of vibrios, V. parahaemolyticus, temperature and salinity detected in both areas. By cultivation, V. parahaemolyticus was regularly observed at Son Bay except in December whereas it was detected only in April and November at Ruesri Bay. The diversity of Vibrio spp. was investigated using the Denaturant Gradient Gel Electrophoresis (DGGE) technique. The diversity of Vibrio spp. detected at Son Bay was homogeneous whereas it was more heterogeneous at Ruesri Bay. Interstingly, in December although V. parahaemolyticus was not detected by cultivation; it was present in this month according to the DGGE technique. Thus, the number of this bacterium was probably low or it was in a non-culturable phase. In this study, V. harveyi was detected in both areas every month by DGGE. This indicates that this bacterium is part of the normal microbiota and is present in the Andaman Sea throughout the year. Correlation between copepods and the numbers of V. parahaemolyticus was not observed in this study.