Abstract: The standard formation free energies at different temperatures of compounds in a Mo-Si-B ternary system were calculated. The adiabatic temperatures and the molten ratios of Mo₅SiB₂(T2 phase) at different initial temperatures for the reaction of synthesizing Mo₅SiB₂ were obtained, The results showed that it was feasible to synthesize in-situ Mo₅SiB₂ from the elemental powders. Mo₅SiB₂ could not be synthesized using the SkIS (self-propagating high-temperature synthesis) mode of combustion. In contrast, the explosion mode of combustion (in-situ reactively hot-pressing) was acceptable. The adiabatic temperature and the molten ratio of Mo₅SiB₂ were relative to the initial temperature.