Grey's mudsnake (Ephalophis greyae), also known commonly as Grey's sea snake, the mangrove seasnake, and the north-western mangrove sea snake, is a species of venomous snake in the subfamily Hydrophiinae of the family Elapidae.

[3] Its specific name, greyae, has also been spelled greyi; however, it was named after a Beatrice Grey who collected the holotype,[4] necessitating a feminine possessive.

E. greyae is found along the northwestern coast of the Australian state of Western Australia, from Shark Bay to Kimberley Region.

[1] The preferred natural habitats of E. greyae are mud flats, salt flats, the marine intertidal zone, and the marine neritic zone, to a depth of 10 m (33 ft).

[1] A small species of sea snake, E. greyae may attain a total length (including tail) of 66 cm (26 in).