Abstract: A ladder stabilizer removably mounts to one of the two spaced rails of a conventional ladder, and a mirror image stabilizer preferably mounts to the other rail. The stabilizer is of unitary construction, preferably injection molded from thermoplastic material, and includes a longitudinal member with an open channel along one longitudinal surface, the channel bounded by opposing longitudinal flanges. The member is sized and shaped and of sufficient flexibility to removably mount to the rail at any desired vertical position, and is relatively non-slidable with respect thereto once mounted. An opposite longitudinal surface of the member includes a plurality of step-like serrations. With one stabilizer mounted to each of the two ladder rails, and the ladder leaned against a structure for conventional use, the step-like serrations reduce the risk of movement of the ladder relative to the structure, and therefore promote safe use of the ladder.