It is necessary to develop nanoperoxidases with high activity to construct a fast and cheap sensing platform for real-time detection of some pollutants. In this study, the as-prepared N and S co-doped core-shell cobaltosic oxide nanospheres (N,S-Co3O4) exhibit excellent peroxidase-like activity. The oxidation reaction of the colorless chromogenic substrate TMB by H2O2 is used to evaluate the peroxidase-like behaviors of N,S-Co3O4. As expected, the N,S-Co3O4 nanospheres accelerated the oxidation of TMB accompanied by a blue shift only in 1 min. Thus, the N,S-Co3O4 nanoperoxidase exhibits high affinity towards TMB (Km = 0.072 mM) and H2O2 (Km = 3.78 mM). Moreover, as the catalytic process of N,S-Co3O4 can be inhibited in the presence of catechol, a fast inexpensive colorimetric sensor of catechol with high sensitivity and good selectivity was constructed. The enhanced catalytic activity of N,S-Co3O4 is attributed to some active species, including h+ and ˙O2-, owing to the more active sites on N,S-Co3O4. The colorimetric method has been validated by detecting catechol in real water samples for practical application.