A slide assembly with a damping device includes a first rail, a second rail, a first support frame, a second support frame, a rack and a damper. The second rail is movable longitudinally relative to the first rail. The first support frame is fixed to the first rail, and the second support frame is fixed to the second rail. The rack is connected to the first support frame. The damper is connected to the second support frame and includes a box and a gear which is pivotally connected to the box. The box includes a damping material received therein. When the second rail is moved relative to the first rail, the gear is driven by the rack and rotates while the damping material provides a damping force to the movement of the second rail.