A retaining mechanism for a slide assembly includes a first rail, a second rail, a holding member, a blocking member and a fixed plate. The second rail is slidably connected to the first rail. The holding member has a fixed end and slots. The fixed end is fixedly connected to the first rail. The blocking member has a fixed end and an engaging section, and is located between the holding member and the first rail. The fixed end of the blocking member corresponds to the fixed end of the holding member and is fixedly connected to the first rail. The engaging section corresponds to the slots of the holding member. The fixed plate is fixedly connected to the second rail and corresponds to the slots of the holding member.