Herein, a new series of magnetic Fe-doped CoO nanocomposites (Fe-CoO NCs) with dual enzyme-like activities (peroxidase and oxidase) were successfully synthesized. The molar ratio of Fe3+/Co2+ salts during the solvothermal process determined the morphology and catalytic activity of the NCs. Among them, the flower-like 0.15Fe-CoO NCs showed high peroxidase-mimicking activity over a wider pH range of 4-5 and a temperature range of 30-50 °C. Such nanozymes were applied for constructing a facile and sensitive colorimetric sensor to detect H2O2 and dopamine (DA) in the linear ranges of 6-20 and 2-10 μM with limits of detection (LODs) of 4.40 and 1.99 μM, respectively. The excellent magnetic separation performance and successful DA detection in human urine samples validated the promising application of CoO-based nanozymes in medical diagnosis. The superior catalytic behaviors of 0.15Fe-CoO NCs could be ascribed to the high surface area, open mesoporous structure, increased surface active species, and the facile redox of Fe3+/Fe2+ and Co3+/Co2+. Based on the results of the fluorescent probe and radical trapping tests, the possible mechanism that Fe doping promoted the decomposition of H2O2 to produce hydroxyl radical (•OH) and superoxide radical (•O2-) was proposed.