An assembly for mounting a vehicle roof-box on a vehicle roof panel comprises a pair of roof rails disposed on the vehicle roof panel at both sides thereof respectively in a front-rear direction of the vehicle roof panel; a plurality of cross-bars spacedly arranged in the front-rear direction, wherein each cross-bar has two opposing ends removably coupled to the roof rails respectively, wherein the vehicle roof-box is mounted to the cross-bars; and a plurality of securing means configured to removably secure the cross-bars to the roof rails, wherein each of the plurality of securing means includes a first bracket movable along each of the roof rails, and a second bracket screw-coupled to the first bracket to secure the first bracket to each of the roof rails, wherein an end of each of the cross-bars is fixed to the second bracket.