The catalytic activities of currently developed peroxidase-mimic nanozymes are generally limited. Therefore, further efforts are still needed to improve the catalytic performance of peroxidase nanozymes. Herein, we synthesized Fe-coordinated carbon nanozyme dots (Fe-CDs) that can serve as both efficient peroxidase nanozymes and -magnetic resonance imaging (MRI) contrast agents. The intrinsic peroxidase-like activity of the Fe-CDs was explored by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (HO). The product showed better performance over natural horseradish peroxidase (HRP) and other mimetic peroxidases. Quantification of glucose and ascorbic acid detection showed that this nanozyme could be used to detect a minimum limit as low as 5 μM glucose. Moreover, the colorimetric detection technique was used to detect serum glucose in mice, and the detection result was comparable with autobiochemistry analyzer results using a glucose assay kit. Furthermore, the Fe-CDs showed good magnetism properties and provided promising MR imaging of tumors with excellent biocompatibility.