This disclosure depicts a construction of a door in a motor vehicle, wherein sliders (14) each having a forward end sliding portion (15) projected into a compartment (16) are secured to end portions of a door glass (12), and the sliding portions (15) of the sliders (14) are slidably guided by guides (20) on a door frame (18) in directions of opening and closing of the door glass (12), whereby the outer surfaces of the door glass (12) and the door frame (18) are substantially flush with each other, and a door mirror (24) is mounted to a triangular portion (22) at a forward end of a window opening. The present invention features that the sliders (14A, 14B, 14C) are provided at three positions including a top end position in a rear portion of the door glass (12), a bottom end position in the rear portion of the door glass (12), which becomes lower than a door beltline (26) in the fully closed state of the door glass (12), and a top end position in a forward portion of the door glass (12), and a forward guide channel (20A) for guiding the slider (14C) at the top end position in the forward portion of the door glass (12) is disposed at a position of the door mirror (24) on the compartment's side and along the rear end edge (24A) of the door mirror (24).