One of the smallest vesper bats, adult little yellow bats measure only 7 to 8 centimetres (2.8 to 3.1 in) in total length, with a forearm about 3 centimetres (1.2 in) long, and weigh just 3 to 8 grams (0.11 to 0.28 oz).

The fur is silky in texture, and fades to a greyer shade on the animal's underside.

[2] Little yellow bats can be distinguished from other members of the genus Rhogeessa by a combination of their size, the presence and amount of fur on the uropatagium, and by the precise shape of their teeth.

[2] Little yellow bats inhabit areas of subtropical vegetation, and have usually been trapped near streams, lakes, or other bodies of fresh water.

[2] It has been reported to be found in areas of mesquite and cactus vegetation, and to be active after sunrise and in the early afternoon.