Most nanozyme research is limited to oxidase and peroxidase. Here, we reported the N, P, or S doped carbon nanotubes (CNTs) for enzyme mimics of nicotinamide adenine dinucleotide (NADH) oxidase and cytochrome c (Cyt c) reductase. Through the doping of N element, the NADH oxidase-like activity of CNTs is highly improved, and the maximum initial velocity for N doped CNT (N-CNT) is increased by 4.28 times compared to that before the modification. Through the analysis of NADH oxidation products, we found that biologically active NAD⁺ was produced, and the oxygen was selectively reduced to water or hydrogen peroxide, which is consistent with natural NADH oxidase. Furthermore, we found for the first time that carbon nanotubes can promote the transfer of electrons from NADH to Cyt c, thereby can mimic the properties of Cyt c reductase.