A new redox polymer containing Os (E-o' = -0.15 V vs Ag\AgCl) was designed and synthesized as an efficient mediator of diaphorase-catalyzed electrochemical oxidation of NADH and as a support to immobilize enzyme(s) on electrode surfaces. The electrochemical characteristics of the polymer and its application to biosensors and bioanodes of biofuel cells are briefed.