The total length of the long-nosed sea snake is 545-707 mm. The snout is long, the head is narrow, the nostrils are dorsal, the nose scales are tangent to each other, the head and neck are not easy to distinguish; the body is flat on the side, and the tail is more flat on the side.

The back of the long-nosed sea snake is black, from the head to the front of the anus, and it is black and wide in the middle The entire tail, back, sides, and abdomen have black patches, and the tail end is also black; both sides and ventral surface are yellow, and the black and yellow are clearly demarcated.