An adjustable bed rail capable of gripping a mattress either alone or together with a bedspring to hold the protective side rail in place. A locking assembly is adjustable to adjust for the height of the mattress either alone or together with the bedspring. Friction pads and/or friction surfaces may be mounted along the bed rail to further enhance the locking of the side rail to the mattress. The bed rail may be provided with a rail that drops down to facilitate climbing on to or off of the bed and can be locked into the upright position.