Abstract: A rail structure for window blinds is provided, which includes a body and at least one connecting member. The body has a pair of first flanges and a pair of second flanges. The first flanges are disposed on tops of two sides of the body, and the second flanges are disposed on bottoms of the two sides of the body. In addition, the connecting member is mounted to an outer surface of one side of the body, has a predetermined shape of constant cross-section profile, a length and a width, Besides, a flange is disposed on a predetermined position of the connecting member and extending to one side of the body. By the connecting members, the headrail appearance can be enhanced. Moreover, as the connecting members do not directly bear the overall or partial weight of the window blind, the rail structure can have an extended product lifetime.