In this study, we investigated a new class of artificial enzymes composed of Mn-porphyrin, imidazole, and cucurbit[10]uril (CB[10]) toward therapeutic antioxidants. Structural characterization by means of NMR indicated that the inclusion mode of metalloporphyrin in CB[10] was sensitive to the chemical structure of metalloporphyrin and that the structure of the artificial enzyme had a similarly to that of native heme catalase. Kinetic analysis for catalytic antioxidative activities demonstrated that the artificial enzyme exhibited highly efficient activity for H2O2 disproportionation (catalase activity) in water. The activity was classified as top-performing among the water-soluble artificial catalases. The artificial enzyme was constructed by simply mixing the components in water. We consider that this is a great advantage over previously reported artificial catalases, which require a multi-step synthesis or that lack water solubility. The pro-oxidative peroxidase activity was remarkably suppressed due to inclusion in CB[10]. Furthermore, a preliminary in vitro study suggested that the artificial enzyme catalytically eliminated reactive oxygen species, including H2O2, in human cell lines. It was presumed that CB[10] contributed to the bioavailability of the artificial enzyme. Overall, the artificial enzyme was shown to have high potential as a therapeutic antioxidant. We consider that the results in this study could lead to a new conceptual advance toward therapeutic antioxidants that could simultaneously improve the catalytic and biological properties of Mn-porphyrins.