The swamp grass babbler or swamp prinia (Laticilla cinerascens) is a small bird of the Indian subcontinent. Some authorities consider it a subspecies of the rufous-vented grass babbler.
Swamp grass babblers average 17 cm long (big for a prinia). Adults are olive-grey above, slightly warmer on the back of the neck and upper back, but less distinctly collared than the rufous-vented grass babbler. Bold dark streaking starts at the forehead and fades on the back. The underparts are greyish white, greyer on the flanks, which may be slightly streaked. There is a faint buff tint to the undertail coverts (but not the distinctive colouring for which the rufous-vented prinia is named). The upper surface of the wings has barring formed by the covert feathers and their paler fringes. The wing linings are a faintly tawny off-white. The flight feathers of the wings are greyish brown; when the wing is folded, the primaries barely extend beyond the tertials. Those of the tail may be greyish or olive-brown and have tawny tips. The tail is long and strongly graduated, that is, the outermost pair of feathers is only one-third as long as the central pair. The head shows a conspicuous white eye-ring, whitish lores, and dark-streaked whitish cheeks.