A new nanocomposite was synthesized by using of carbon dots and magnetic nanoparticles as precursors. TEM images and spectra of FT-IR, XRD and EDS confirmed the presence of nanocomposite in the solution. The synthesized nanocomposite shows intrinsic peroxidase-like activity. The main advantage of synthesized nanocomposite is its higher peroxidase-like activity rather than both individual C-dots and magnetic nanoparticles. Also, the introduced nanocomposite was used for colorimetric determination of hydrogen peroxide with linear range of 1.0×10−8M to 1.0×10−3M and LOD of 1.0×10−9M.