Abstract: To provide basic data for sustainable management of the coastal ecosystem，the community structure of phytoplankton and the associated environmental factors were investigated in the coastal waters of Leizhou Bay of Guangdong from February to November in 2013.There were totally 142 species recorded，with 116 species in 42 genera of Bacillariophyta，accounting for 81.3% of the community，and 19 species in 10 genera of Pyrrophyta，accounting for 13.8% of the community，5 species in 5 genera of Cyanophyta，accounting for 3.5%，and other 2 species only accounting for 1.4%. Most of dominant species were low saline species characterized of a sub-tropical and nearshore community except for a few open sea species. There were neither obvious seasonal dominant species nor annual wide spread dominant species. The average abundance of phytoplankton was 12.92×10⁴ cell/dm³ ranged from 0.26×10⁴ to 60.35×10⁴ cell/dm³，with the highest density in autumn，followed by winter，summer and spring in consequence. In addition，the greatest abundance of species was observed in the central area and lower abundances were in the top and the mouth of Leizhou Bay. The abundance of phytoplankton was correlated negatively to the water temperature with a coefficient of-0.415 （p<0.05，n=36，two-tailed t test） and no significant correlations （p>0.05） founded with other environmental factors. The community structure of phytoplankton in the coastal waters of Leizhou Bay changed substantially compared with that of 1987 as species numbers and dominant species increased by 61.4% and 100%，respectively，besides a 30 times of abundance increment，which indicates a healthy and stable community by its complexity.