A window blind assembly includes a curtain having multiple partitioning portions, and a curtain control unit for bringing the curtain to fold upwardly and unfold downwardly. The curtain control unit includes a winding rod, a blind piece wound around and extended from the winding rod, and a plurality of connecting members each mounted on a respective one of the partitioning portions. Each connecting member and a corresponding partitioning portion define a slot therebetween. Each connecting member includes a connecting strip, a support rod mounted at the connecting strip to stiffen the connecting strip, and a fastener for removably fastening the connecting strip to the corresponding partitioning portion.