Morphological changes in various water depths of Enhalus acoroides (L.f.) Royle were studied at Hat Chao Mai National Park, Trang province. Plant specimens were collected by Line-transect method (1 transect). The sampling plots were collected at 100, 200,300, 400, 500 and 600 meters from coast (1.2, 1.5, 1.7, 1.9, 2.0 and 2.1 meters water depth,respectively). It was found that the maximum rate of sexual reproductions was found at 1.5 meters water depth (200 meter from coast). The maturation of flowers andthe pollination occurred during the low tide. Mature fruit ruptures along the septum. The new shoots can regenerate from underground stem at all depths. The morphological changes of E. acoroides had been studied and found that the diameter of root and stem and root length tends to reduce when the depth of water increase, but statistically, were not significant. The number of leaf and leaf width tends to reduce when the depth of water increase. Contradictory to the leaf length that increases when the water depth increase which had a significant differences at 95%