Biodiversity "hotspot" areas have been shown to possess unique diatom floras. During our diatom studies of some of these types of areas in China, samples were collected from Hainan and Guangdong Provinces, and four species from 4 different genera are proposed as new to science based on LM and SEM observations. These new taxa are Eunotia dinghunsis Liu & Kociolek, sp. nov., Brachysira subirawanae Kociolek & Liu, sp. nov., Microcostatus muscus Liu & Kociolek, sp. nov. and Iconella sanyatangum Liu & Kociolek, sp. nov. In addition, a species known previously only from Java and Sumatra, Pinnularia rivularis Hustedt, was observed, and herein we provide LM and the first SEM observations of this species.