A cordless curtain assembly includes a curtain body connected between the head box and the bottom bar. A controller, a fixed unit and a movably unit are located in the head box. The movable unit is movably located between the controller and the fixed unit. A driving rope has a first end fixed to the bottom bar and the second end of the driving rope goes through the curtain body and the head box, and is wrapped to the guide members of the movable unit and the fixed unit. The second end of the driving rope then extends through the head box and through the curtain body and is eventually fixed to the bottom bar. A resilient rope has one end fixed to the movable part and the second end of the resilient ripe goes over the pulley in the controller and is fixed to the fixed unit.