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Inorganic nanomaterials with enzyme-like activity have been attracting much attention due to their low cost, favorable stability, convenient storage, and simple preparation. Herein, Co 3 O 4 nanoplates with a uniform nanostructure were prepared by the thermolysis of cobalt hydroxide at different temperatures, and the influence of the annealing temperature on the performance of the mimetic enzyme also was reported for the first time. The results demonstrated that Co 3 O 4 nanoplates obtained at an annealing temperature of 200 °C possessed strong oxidase activity and efficiently catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) without the addition of hydrogen peroxide to generate the blue color product ox-TMB. Once the annealing temperature was increased to 500 °C and 800 °C, the oxidase activity of Co 3 O 4 decreased rapidly, and was even inactivated. This might be attributed to the relatively large specific surface area of Co 3 O 4 annealed at 200 °C. Besides this, based on the TMB-Co 3 O 4 nanoplate system, a colorimetric analysis method was developed to detect dopamine with a limit of 0.82 μmol/L in a linear range from 1.6 μmol/L to 20 μmol/L., Competing Interests: The authors declare no conflict of interest.