Waterbirds and their seasonal dynamics in 17 mangrove wetlands including Mingren, Huiwen, Xiaohai, Li’angang, Tielugang, Yuya, Qiugang, Yinggehai, Shan′gao, Sigeng, Changhuajiang, Haiwei, Yangpugang, Xinying, Huaguo, Dongzhaigang and Sanjiang (Fig. 1) in Hainan Island, China, were surveyed from November 2015 to June 2016 with binoculars and monocular telescopes by line transects and point counts methods. A total of 74 waterbird species of 5 orders and 12 families were recorded (Appendix 1), among which the Common Shelduck (Tadorna tadorna) was recorded for the first time in Hainan Island. The Xinying Bay in Danzhou was found as a new wintering site for the Black-faced Spoonbill (Platalea minor). The Shannon-Wiener index, Pielou index and Jaccard index were measured to identify the waterbird diversity. Shorebird species were accounted for the largest proportion in autumn (10.9%), winter (28.3%), spring (31.5%) and summer (20.8%). The number of shorebirds was the largest proportions in winter (55.7%) and spring (47.6%), however, the number of herons being the largest proportion in autumn (48.6%) and summer (41.5%)(Table 1). The sites with the largest number of waterbirds were Xiaohai of Wanning, Dongzhaigang of Haikou and Yinggehai of Ledong. The sites with the species richness of waterbirds were Dongzhaigang, Sigeng, Yinggehai, Xinying, Changhuagang, Yuya and Huiwen (Table 2). The Pielou index in Huaguo, Shan′gao, Dognzhaigang and Yingehai was higher (Table 2). Dongzhaigang has the highest Shannon-Wiener index and Pielou index. The analysis showed the higher Jaccard comparability index in similar habitats, with Huaguo and Mingren showing more species similarity (Table 4). The abundance and richness of waterbirds showed seasonal dynamics with more species and higher abundance detected in autumn and winter. Our study suggest that coastal mangrove wetlands are important habitats for waterbirds, and protecting mangroves wetlands being a key role in conservation of waterbirds.