A model describing the in-flight evaporation of particles injected into a high-temperature plasma jet issuing into surrounding air has been developed and incorporated into an earlier model that includes a detailed description of particle heating and melting. In addition to physical evaporation controlled by vapor diffusion and heat transfer, the evaporation due to the production of volatile oxides on the particle surface is also modeled. The effect of evaporation-induced mass transfer on heat flux to the particle surface is taken into consideration along with the effects of variable plasma properties and the modification of heat and momentum transfer due to non-continuum effects experienced under plasma conditions. Computational results on molybdenum particles in an argon-hydrogen DC plasma spray system are developed and are qualitatively compared with experimental results.