A belt line portion sound insulation structure for an automobile between a door panel and door glass includes a viscoelastic member arranged on a lower portion of one of principal faces of a glass plate of the door glass. The door panel includes two panel plates facing each other, and the door glass is arranged between the two panel plates so as to be movable up and down. A hardness measured on a surface of the viscoelastic member is 10 to 80 in an Asker C hardness defined by SRIS 0101. In a closed state of the door glass, the viscoelastic member is restrained by a portion of a surface of one of the two panel plates facing the one of the principal faces and an area on one of the two panel plates where the viscoelastic member is disposed.