The thermal properties of cordierite (2MgO.2Al2O3.5SiO2)+30 wt% clay+ Xwt% MnO2 of infrared radiator have been investigated as a function of MnO2 additives (X=0,0.1,0.25,0.5,1.0,1.5,2.0,2.5). The thermal expansion coefficient was decreased with increasing amounts of MnO2 additives. Otherwise, the spectral emissivity was increased in the below 4.5 ${mu}{ extrm}{m}$ wavelength. Also, the infrared radiator of cordierite system which spectral emissivity was approximately 1.0 can be attainable at from 4.5 ${mu}{ extrm}{m}$ to 8 ${mu}{ extrm}{m}$ wavelength. The spectral emissivity was decreased from 8 ${mu}{ extrm}{m}$ to 14 ${mu}{ extrm}{m}$ above X=2.5.