A tooth-whitening gel is provided. The main component of the tooth-whitening gel comprises a polypeptide having halamine (N-X bond, X=Cl, Br or I) groups and a high molecular weight. By the redox properties of halamine group, the pigment molecule over the teeth’s surface can be bleached and faded to whiten the teeth.一種牙齒美白凝膠,其中主要成分包含一種具有高分子量及鹵胺(N-X,X=Cl,Br or I)官能基的多胜肽。藉由鹵胺的氧化還原特性,使牙齒表面的有色物質漂白褪色,進而達到牙齒美白的功效。