5‐Ethylphenazine ‐ poly(ethylene glycol) ‐ NAD+ conjugate (EP+‐PEG‐NAD+) was prepared by linking 1‐(3‐carboxypropyloxy)‐5‐ethylphenazine (I) to poly(ethylene glycol)‐bound NAD+ (PEG‐NAD+) and its kinetic properties were studied. As a reference compound, poly(ethylene glycol)‐bound 5‐ethylphenazine derivative (III) was also prepared and the effects of poly(ethylene glycol) on the reaction rate of the 5‐ethylphenazine moiety with NADH was investigated. The second‐order rate constant, k1, of the reaction of III with NADH is 2.78 mM−1 s−1 and is about 1.7 times that of 1‐(3‐ethoxycarbonylpropyloxy)‐5‐ethylphenazine (II) with NADH. A similar effect of the attached poly(ethylene glycol) was observed for the reaction of PEG‐NADH with I or II. The second‐order rate constants, k2 and k3, of the reactions of the reduced form of III with oxygen and with 3‐(4′,5′‐dimethylthiazole‐2‐yl)‐2,5‐diphenyltetrazolium ion, respectively, were k2= 1.22 mM−1 s−1 and k3= 32 mM−1 s−1; the k2 value is not changed but the k3 value is decreased by the attachment of the polymer.EP+‐PEG‐NAD+ works as a unique catalyst having an intramolecular reaction step within its turnover cycle in a coupled multi‐step reaction system containing malate dehydrogenase, malate, EP+‐PEG‐NAD+, a tetrazolium salt and oxygen. The first‐order rate constant, k4, of the intramolecular reaction was 1.1 s‐1. The effects of the covalent linking of the 5‐ethylphenazine and the NAD+ moieties were estimated by comparing the value of k4 with that of k1 for the reaction of III with NADH; the effective concentration of the NADH moiety for the 5‐ethylphenazine moiety on the same EP+‐PEG‐NADH molecule (or vice versa) was calculated to be 0.40 mM from the ratio of k4/k1. The values of the rate constants in the coupled multi‐step reaction system enable us to understand the dynamic features of the system and the characteristics of EP+‐PEG‐NAD+ as a catalyst are discussed.