The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser was measured for the middle infrared waveband at temperature range 100 to 200°C. Compared to that of flat silicon, emissivity was enhanced over the entire wavelength range. For a sample with different spike height, the minimum emissivity at a temperature of 100°C is more than 0.6. Although the average emissivity is less than Nextel- Velvet-811-21 Coating , it can be used stably at more wide temperature ranges. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based devices.