A window blind assembly adapted for being mounted to a window, comprising: a roller blind unit including a roller rod that extends horizontally and that is rotatably mounted at or in proximity to an upper edge portion of the window, and a roller blind piece a top edge of which is connected to said roller rod and which is able to be wound around and extended from said roller rod; a curtain member unit including a curtain member, said curtain member having a sheltering portion a top edge of which is mounted at or around the upper edge of the window, and a plurality of partitioning portions that extend horizontally, are respectively connected to a rear surface of said sheltering portion, and are vertically spaced apart from each other; and a clamping unit including a plurality of connecting members associated respectively with said partitioning portions, each of said connecting members having a confining portion, and two securing portions connected to opposite ends of said confining portion and that connect said confining portion to a respective one of said partitioning portions, said confining portion, said securing portions, and said partitioning portion defining a slot thereamong for extension of said roller blind piece therethrough; when said roller blind unit is manipulated such that said roller blind piece is wound around said roller rod, said sheltering portion is displaced upwardly, thereby folding said sheltering portion; characterized in that: said roller blind unit further includes an auxiliary roller blind piece a top edge of which is connected to said roller rod and which is able to be wound around and extended from said roller rod in a direction opposite to winding and extending of said roller blind piece; said curtain member unit further includes an auxiliary curtain member, said auxiliary curtain member having an auxiliary sheltering portion a top edge of which is mounted at or around the upper edge of the window, and a plurality of auxiliary partitioning portions that extend horizontally, are respectively connected to a front surface of said auxiliary sheltering portion, and are vertically spaced apart from each other; and said clamping unit further includes a plurality of auxiliary connecting members associated respectively with said auxiliary partitioning portions, each of said auxiliary connecting members having an auxiliary confining portion, and two auxiliary securing portions connected to opposite ends of said auxiliary confining portion and that connect said auxiliary confining portion to a respective one of said auxiliary partitioning portions, said auxiliary confining portion, said auxiliary securing portions, and said auxiliary partitioning portion defining a slot thereamong for extension of said auxiliary roller blind piece therethrough; when said roller blind unit is manipulated, a moving direction of said auxiliary sheltering portion is opposite to that of said sheltering portion. a roller blind unit including a roller rod that extends horizontally and that is rotatably mounted at or in proximity to an upper edge portion of the window, and a roller blind piece a top edge of which is connected to said roller rod and which is able to be wound around and extended from said roller rod; a curtain member unit including a curtain member, said curtain member having a sheltering portion a top edge of which is mounted at or around the upper edge of the window, and a plurality of partitioning portions that extend horizontally, are respectively connected to a rear surface of said sheltering portion, and are vertically spaced apart from each other; and a clamping unit including a plurality of connecting members associated respectively with said partitioning portions, each of said connecting members having a confining portion, and two securing portions connected to opposite ends of said confining portion and that connect said confining portion to a respective one of said partitioning portions, said confining portion, said securing portions, and said partitioning portion defining a slot thereamong for extension of said roller blind piece therethrough; said roller blind unit further includes an auxiliary roller blind piece a top edge of which is connected to said roller rod and which is able to be wound around and extended from said roller rod in a direction opposite to winding and extending of said roller blind piece; said curtain member unit further includes an auxiliary curtain member, said auxiliary curtain member having an auxiliary sheltering portion a top edge of which is mounted at or around the upper edge of the window, and a plurality of auxiliary partitioning portions that extend horizontally, are respectively connected to a front surface of said auxiliary sheltering portion, and are vertically spaced apart from each other; and said clamping unit further includes a plurality of auxiliary connecting members associated respectively with said auxiliary partitioning portions, each of said auxiliary connecting members having an auxiliary confining portion, and two auxiliary securing portions connected to opposite ends of said auxiliary confining portion and that connect said auxiliary confining portion to a respective one of said auxiliary partitioning portions, said auxiliary confining portion, said auxiliary securing portions, and said auxiliary partitioning portion defining a slot thereamong for extension of said auxiliary roller blind piece therethrough;