Submicron metallic slit arrays with different geometry were designed and fabricated on silicon substrates. Their infrared radiative properties (transmittance, reflectance, and absorptance) were investigated both experimentally and theoretically. The normal transmittance of three fabricated Au slit arrays was measured at wavelengths between 2 mu m and 15 mu m using a Fourier-transform infrared spectrometer. The experimental results were compared to the values calculated from the rigorous coupled-wave analysis. The applicability of the effective medium theory for modeling radiative properties was also examined. The agreement between the measurement and modeling results demonstrates the feasibility of quantitative tuning of the radiative properties by employing periodic micro/nanostructures.