Nassarius thachi is a species of sea snail, a marine gastropod mollusk in the family Nassariidae, which includes the nassa mud snails and dog whelks. There is no official common name for this species.
The shell is an elongated egg shape with ribbing, measuring approximately 25-36 mm long; however, larger specimens can reach 38 mm in length. They are usually light brown to grayish brown with two to three darker brown broad spiral bands. The inside of the shell is light cream to white in colour.
This species occurs in the tropical Western Pacific off China, Taiwan, Vietnam, Indonesia, Fiji.