Leptobrachella mjobergi is found in low elevation primary, secondary and even disturbed forests. We encountered it from near sea level to 500 m asl. They reach approximately 20 mm in both sexes.It lives along small streams with moderate current. Males sit on the banks or on low vegetation (5–30 cm) when calling.

This frog is brown above with dark markings between eyes, on the shoulder, and thighs. The supratympanic fold is not distinct in coloration. The flanks bear white glands that can fuse to to a longitudinal ridge. Toe and finger tips are pointed. Foot webbing is absent.

This little frog has a very loud, high frequency buzzing call. Approaching a calling male closely can be very unpleasant in the ear. 

L. mjobergi prefers streams with finer gravel than baluensis. Little is know about the life habits of the tadpoles, which live in the gravel interstices. Larvae reach 40 mm in length. 

The tadpole's body shape is typical for a Leptobrachella: it is very slender, has a funnel mouth, and a very long tail. They move in a characteristic undulating fashion. Head and trunk radius of action exceed those of other tadpoles.