Microdrillia fastosa is a species of sea snail, a marine gastropod mollusk in the family Borsoniidae.

(Original description) The shell is small, rather solid, slender and has a fusiform shape.

This is followed by a broad concave fasciole, margined in turn by a sharp projecting keel which determines an angle in the contour of the shell.

On the body whorl there are about fourteen spirals, gradually diminishing anteriorly, below the major keel.

The rest protrude medially, and are crossed by fine sharp radial riblets, which on the last whorl number twenty-two.