Rufous-vented grass babblers average long with a wing length from the bend to the tip of (females) or (males) to . Adults are a cool brown colour above except that a buffy region on the back of the neck and upper back forms a distinct collar. Bold dark streaking starts at the forehead and fades on the back. The underparts are whitish with a tawny hue and dark streaking on the flanks. The undertail coverts are bright rufous or chestnut. 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 rufous 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.