Fe₃C and Mn doped Fe₃C nanoparticles (NPs) were prepared by a sol–gel method. The structures, morphology and magnetic properties are researched. From Transmission Electron Microscopy (TEM) results, it is shown that the morphology of the Fe₃C and Mn doped Fe₃C NPs are different. From vibrating sample magnetometer (VSM) results, it is indicated that their special saturation magnetization (Ms) values tend to decrease with increasing the Mn doping concentration, which can be correlated with changes in the lattice constant due to the Mn ion incorporation in Fe₃C.