Infrared radiators of a cordierite system [cordierite (2MgO.2Al2O3.5SiO2)＋30wt% clay＋X wt% MnO2 (X=0, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5)] were manufactured by a slurry casting method. Thermal and physical properties of these infrared radiators were studied by the measurement of spectra emissivity, thermal expansion coefficient and apparent density, SEM and EPMA analyses were also carried out. The thermal expansion coefficient and apparent density were decreased with increasing amouonts of MnO2 additives. On the other hand, the spectral emissivity was increased in the wavelength below 4.5${mu}{ extrm}{m}$. Also, infrared radiators of the cordierite system, of which the spectral emisivity was 0.8, could be attainable in the wavelength above 4.5${mu}{ extrm}{m}$. The infrared radiator of the cordierite system with 2.0wt% MnO2, of which the spectral emissivity was approximately 1.0, could be attainable in the wavelength between 4.5${mu}{ extrm}{m}$ and 8${mu}{ extrm}{m}$. The spectral emissivity of the specimen containing 2.0wt% MnO2 was higher than others in the wavelength between 8${mu}{ extrm}{m}$ and 14${mu}{ extrm}{m}$.