Microhyla perparva is a very small frog species that inhabits the forest floor. Females reach a maximum snout–vent length of about 15 mm, though males are smaller, typically ranging from 10 to 13 mm. This species is smaller than the similar Microhyla petrigena.

The dorsal coloration consists of various shades of brown, often featuring dark markings on the shoulders and a light-colored band along the flanks. The first finger is greatly reduced, leaving only three fully developed fingers on each hand. The toe tips are expanded, a common feature in the genus.

Although locally abundant, M. perparva is seldom encountered in the leaf litter. However, after heavy rains, hundreds of males may emerge and gather in water-filled depressions. We observed breeding groups during the day; they presumably breed at night as well. Males float at the surface of shallow pools with their vocal sacs inflated, calling from small territories. They attempt to clasp any passing females and aggressively fend off rival males.

The tadpoles of this species are extremely delicate and mostly transparent. When viewed from above, they appear dark grey. A distinctive brown cross-band is present near the distal third of the tail, which ends in a slender flagellum. These tadpoles are suspension feeders that occupy the middle of the water column. They lack keratinized mouthparts; instead, they have a terminal mouth and a spiraculum located medially on the ventral side. When undisturbed, they move very slowly, propelling themselves with gentle beats of the tail flagellum. The eyes are positioned laterally on the head.