Thermal spray coatings can be a response to corrosion and wear problems of steel parts, with the benefit of applying various coating materials. So far, many efforts have been made to improve the properties of nickel-aluminum thermal spray coatings, including the use of different thermal spraying methods and grain size control, but no heat treatment was performed on these coatings and no evaluation of its effect on the coating properties was made. Performing heat treatment after spraying process to create metallurgical bonding between coating/substrate and to create a desirable stable intermetallic structure in the coating in order to against high-temperature oxidation, is an effective way. The reason for using nickel-aluminum coating is good wear resistance, excellent corrosion resistance and high-temperature oxidation along with low production costs. In this study, the effect of time and temperature of heat treatment on Ni-20 wt.%Al flame spraying coatings has been studied to improve oxidation Resistance. Coatings were applied on the ST37 steel substrate by a flame spray method. After spraying processes, the specimens were capsulated in a quartz glass and were heat-treated in vacuum at 850°C and 950°C for 1 hour and also at 1050°C for 1, 3 and 6 hours. To characterize the microstructure of the coatings, Scanning Electron Microscopy (SEM) and Energy Distribution Spectrometer (EDS) were used. Also, phase analysis was performed by X-ray diffraction (XRD). The results showed that the heat treated sample at 1050°C for one hour had the lowest porosity and the highest NiAl phase compared to the rest of the coatings. Therefore, this sample as an optimal heat treated sample was exposed to the ambient air at 400, 600, 800°C, for the oxidation test, along with spray and bare steel samples. The results showed that the oxidation rate constant (kp) for the heat treatment, the as sprayed and the bare steel samples are 24.66, 65.05 and 269.42 mg 2 /cm 4 h respectively, in a result the Kp value for the heat treated sample was lower compared to the as sprayed coating and the bare steel; therefore It has a higher thermal resistance. This affair are attributed to the higher presence of NiAl intermetallic compound, less porosity and Formation of Al2O3 denser single-layer oxide on the surface. Keywords: Low carbon steel Heat treatment, Thermal spraying, Oxidation resistance, Nickel-aluminum coating