Nanozymes hold huge potential in various fields, but their much lower catalytic activities than natural enzymes greatly limit their extensive applications. Recent studies indicated that an enhanced enzyme-like activity could be obtained by decreasing the particle size through rational design because smaller nanoparticles (NPs) have larger surface-area-to-volume ratios and more unsaturated sites, which are beneficial to the adsorption of reactant species. However, ultrasmall NPs have low adsorption energy and poor stability, which makes the synthesis of superstable and ultrasmall nanozymes extremely difficult. Several interesting works reported that the encapsulation of ultrasmall NPs with few-layer carbon shells could effectively protect them from dissolution and agglomeration, and meanwhile, their catalytic activities were not greatly affected. Herein, we report a superstable and ultrasmall graphene encapsuled CoRu nanocrystal (CoRu@G) with the CoRu alloy confined in the nanospace of few-layer graphene via the chemical vapor deposition method. It shows excellent corrosion resistance in aqua regia due to the protection of the chemically inert graphitic shell. The intrinsic peroxidase-, oxidase-, and catalase-like activities of the CoRu@G are systematically explored, including the influence of the concentration, pH, and temperature on the enzyme-like activity, steady-state kinetic analysis, and catalytic oxidation mechanism study. Significantly, the CoRu@G shows an excellent and ultrastable enzyme-like activity with the treatment of high temperatures, buffered solutions, or NaCl solutions probably because the graphene layer protects it from dissolution and agglomeration efficiently. We believe that the proposed graphene confinement strategy could highlight the direction of highly active, superstable, and ultrasmall-sized nanozyme preparation.