Abstract: An improved decorative trimming system for installing crown mold, baseboard and the like to a room includes elongated mounting brackets adapted to be secured along room walls extending about the room periphery. Each bracket include a projecting tongue that extends along the length of the bracket. Prefabricated corner pieces of molding are provided with longitudinal grooves extending along the back sides of their legs for receiving the tongues of the mounting brackets in snug fitting relationship. Similarly, straight lengths or strips of molding have grooves formed along their back sides also for receiving the tongues of the mounting brackets. In use, mounting brackets are secured along room walls extending about the room periphery and prefabricated corner pieces are pressed or snapped into position on the mounting brackets.