In this study, B 4 C–Ni and B 4 C–TiB 2 –TiC–Ni composite coatings were thermally sprayed on the surface of 4130 steel substrate by a high velocity oxy-fuel (HVOF) torch. Before the HVOF process, the B 4 C–Ni and B 4 C–TiB 2 –TiC–Ni composite powders were prepared by mechanical alloying (MA) and spray drying processes. In order to study the oxidation behavior of coatings, thermo-gravimetric analysis (TGA) was done at three temperatures of 500, 700 and 900°C for 35h. Structural evolution of powder particles and coatings was investigated by X-ray diffractometry (XRD). The morphology and microstructure of powder particles and the coatings were studied by scanning electron microscopy (SEM). It was found that during TGA experiments of B 4 C–Ni coating, spallation was occurred at all temperatures, indicating the formation of non-protective oxide scale on the surface of this coating. First oxidation and then with increasing time, spallation were the predominant processes at 700 and 900°C. No spallation was seen in TGA experiments of B 4 C–TiB 2 –TiC–Ni coating. Formation of the protective oxide scale on the surface of this coating decreased the oxidation rate with increasing time.