An adjustable neck brace is provided, including: a neck collar, including a sliding engaging groove, the sliding engaging groove extending in an extension direction and having a first engaging portion； a single positioning member, attached to the neck collar and movable along the sliding engaging groove, having a second engaging portion, the second engaging portion being releasably positioningly engaged with the first engaging portion； a chin support, relatively movably connected to the neck collar； at least one connecting member, connecting the positioning member and the chin support.
