Abstract: River sand resource is increasingly scarce compared with dramatic abundance of sea sand resource in Hainan island. Most of coastal engineering projects are sea sand foundation. But so far, there are limited systematically research results on physical and mechanical properties of sea sand in Hainan. This paper deals with a comparative study on physical and mechanical properties of sea sand. Laboratory tests are conducted on samples from 13 bays around Hainan. The results show follows, the silt content of all sand samples satisfy the standard of sand for construction. Most of samples are poorly graded except the grain composition of Yulinzhou is well graded. All the samples from the eastern beach belong to the medium sand and fine sand, while the main ingredient of west beach is coarse sand. Every sample compactness can achieve dense state under smaller preloading(50kPa), but more than half ones just have changes slightly under preloading pressure between 50kPa to 100kPa. They change a lot when the preloading increase from 100kPa to 200kPa. The internal friction angles of samples fluctuate about 25% from 39.24°to 48.24°. The trend of fluctuations is consistent with the mean grain size. The difference of salt content between samples is huge. The maximum one of Jinhai Bay, 3.1g·kg^-1, is almost eight times of that of Lingshui Bay, 0.4g·kg^-1(the minimum value).Besides the sand of Qingshui Bay, all sample salt contents of other bays are much higher than the national standard of six over ten thousand. So they must be desalinated if they are used as construction sand.