Solid state reactions between Ir and SiC and between Ir and Y2O3 were studied. The thermodynamics and mechanism of solid state reaction were discussed. The results indicate that Ir reacts with SiC at 1000 °C to yield Ir3Si and graphitized carbon. The products of Ir silicide changes from Ir3Si and IrSi at 1200 °C to IrSi at 1400 °C. The solid state reaction between Ir and Y2O3 is thermodynamically favorable above 1800 °C in a reductive carbon atmosphere. The reaction mechanism between Ir and Y2O3 was analyzed based on the Engel correlation between electronic configuration and structures of metals and alloy crystal structure.