Benthic diatoms are as important as the planktonic diatoms in the water column. Although benthic diatoms are quite well documented in most aquatic ecosystems, studies on their species composition on the offshore seafloor are very limited. Therefore, this study was conducted to preliminary determine the diversity of benthic diatoms, which is the most ubiquitous group of the microphytobenthos (MPB) collected on the seafloor of the southern South China Sea along the Peninsular coastal waters during a research expedition in March 2019. Triplicate samples were collected from six stations (E1 to E6) and a total of 968 cells representing 17 species of benthic diatoms were identified and recorded. The highest species richness was recorded at E1, with 16 species, and the least number of species was found at E6, with nine species. The highest density was recorded at E3 with 30 cells cm-2 and the lowest density was found at E6 with only three cells cm-2. Coscinodiscus sp. was the most abundant species. Although only preliminary, this study provides essential baseline data, especially due to limited information available on the diversity and richness of benthic diatom in the coastal waters of the South China Sea.