Mangelia decaryi is a species of sea snail, a marine gastropod mollusk in the family Mangeliidae.

This rather solid shell had a high spire with 8 convex whorls, separated by a distinct suture.

The others show axial plicae that are a little arcuate and become sigmoid on the body whorl.

The outer lip is incrassate, bends off inwards and ends at the top into a large and deep sinus.

The color of the shell is white, banded in the upper whorls by a series of brown spots between the axial plicae.