A self-locking slide rail device with buffer mechanism includes a slide rail, a fixing seat, a sliding seat, a hook member, two springs, a connecting member, and a buffer. The slide rail includes an outer rail and an inner rail. The fixing seat is disposed on a rear end of the outer rail, and has a body portion and a guiding extension portion. The sliding seat is disposed on the guiding extension portion. The hook member is disposed on the sliding seat. The two springs are disposed in parallel with each other on the fixing seat. The connecting member is disposed on the inner rail to interlink with the hook member. The buffer is disposed on the center of the body portion.