To provide a flexible slide rail stopper made of synthetic resin generating no metallic sound, without difference between left and right side, capable of being surely engaged and through each operation disengaged.

Concerning a pair of resin stopper members 10 for slide rail, a lock projection is provided on the side of a fixed rail, and an abutting projection 22 composed of a flexible synthetic resin the slender piece 20 is provided on the side of a movable rail so as to freely cancel rocking. Then, one end of the slender piece is forked for the width of the rail, and the other end is formed into pressing enable sharpened part 20a. Then, the rear face of the lock projection facing an abutting face 22a is triangularly notched, the rear side of the abutting projection confronted with the abutting face is triangularly notched as well and when the rail is slid and inserted, the rear end of abutting projection of the slender piece and the rear end of lock projection of the lock piece are locked and pass each other.