An opening device for a slide assembly includes a swing member with a pin portion, a first resilient member and a pusher connected to the first rail. The first resilient member applies a force to the pusher. An engaging member pivotably connected to the second rail and includes a block and a positioning leg contacting a portion of the second rail. The engaging member is connected to a second resilient member. When the second rail is retracted relative to the first rail, the block of the engaging member contacts the pin portion of the swing member. When a pull force is applied to the retracted second rail, the engaging member swings an angle on the second rail to disengage the block from the pin portion of the swing member, and the engaging member returns to its original position relative to the second rail.