An anti-separating mechanism for preventing a fastener strip from separating from a fastener gun is disclosed. The anti-separating mechanism is disposed in the fastener gun. The fastener gun includes a gun body, a fastener magazine and a feed member. The gun body includes a firing channel to receive a fastener. The fastener magazine is connected to the firing channel and is utilized to guide the fastener strip including a plurality of fasteners. The feed member is utilized to push the fastener strip in a first to direction toward the firing channel. The anti-separating mechanism includes a lever pivotally disposed on the fastener magazine. The lever swings between a stop position and a release position. The lever includes a stop surface, a withstanding portion and a tapered pushing surface. The tapered pushing surface is farther from the firing channel than the stop surface.