This paper presents a mathematical model of the in-flight thermal behavior and oxidation of powder particles during thermal spray deposition. In particular, stainless steel and Cr3C2-NiCr particles are investigated. The in-flight model accounts for the acceleration and deceleration of the particles during flight under variable fluid velocity, while the thermal model takes into account heating, melting, cooling and possible solidification as the particle travels towards the substrate. A finite difference method is used to solve the thermal energy conservation equation of the particles. The model includes non-equilibrium calculations of the phase change phenomena in the liquid-solid (mushy) zone and dissolution of the ceramic reinforcement in the composite particles. The growth of the oxide layer at the particle surface is represented by a modified boundary condition, which includes finite-rate oxidation. The results obtained give the interrelations between various process parameters and the oxidation phenomenon.