A synchronous mechanism of a slide rail includes a first hooked bracket, a second hooked bracket, an inner hook set and an outer hook set. The first hooked bracket and the second hooked bracket are installed on a middle rail, and the inner hook set is installed on an inner rail, and the outer hook set is installed on an outer rail. When the slide rail is pulled out or pushed in, the inner, middle, and outer rails are interacted, so that the inner rail, the middle rail and the outer rail can be moved synchronously when they are pushed in or pulled out, so as to improve the smoothness and stability of the operation and the practicality and service life of the product.