A sunroof decoration cover assembly includes: a guide rail frame provided with a guide rail and coupled to a vehicle body; an operational mechanism, which is operated along the guide rail to open and close a sunroof window unit; a front assembly portion formed on the operational mechanism; a rear assembly portion provided with a drip rail coupled to the guide rail frame; a sunroof decoration cover supported by a sunroof decoration cover guide and covering the operational mechanism; a front assembly unit provided on the sunroof decoration cover guide and coupled to the front assembly portion; a rear assembly unit provided on the sunroof decoration cover guide and coupled to the rear assembly portion; and an upper coupling unit provided on the upper portion of the sunroof decoration cover and coupled to the sunroof window unit.