A guide rail assembly for slidably opening and closing a drawer within an enclosure is disclosed. The assembly comprises a mounting bracket (10) for fixing the assembly to the enclosure, a fixed rail (20) on the mounting bracket for receiving an intermediate rail (30), an intermediate rail capable of sliding back and forth relative to the fixed rail, an outer pull out guide (40) for attachment to the drawer and being capable of sliding back and forth on the intermediate rail relative to the intermediate rail and the fixed rail, a protrusion (43) on the bottom surface of the outer pull out guide, a damping device (80) and a channel guide (60) disposed along the mounting bracket adjacent the fixed rail. The damping device is resiliently compressible in a lengthwise direction and the channel guide is provided with a sliding member (70). The sliding member includes an inner portion (71) that travels within the guide and an outer portion (72) that extends outwardly from the guide so as to be contactable by the pull out guide protrusion. The inner portion of the sliding member locates an end (82) of the damping device that can be pushed inwardly to provide damping. During a closing action of the assembly, the outer pull out guide is caused to slide in a drawer-closing direction and when the protrusion reaches and contacts the sliding member outer portion, the sliding member travels within the channel guide against the resilience of the damping device and causes deceleration of the drawer-closing motion.