Abstract: Aspergillus niger spores is an important part of bio-aerosols, and its mass extinction coefficient is an important parameter for study on electromagnetic attenuation characteristics of aspergillus niger spores. The reflection spectra before and after aspergillus niger spores inactivation within the 2.5-15 um waveband were measured by squash method. The complex refractive index of aspergillus niger spores in the infrared waveband was calculated by using Kramers-Kroning (K-K) relation. Then, based on Mie scattering theory, the mass extinction coefficient before and after aspergillus niger spores inactivation in the infrared waveband were obtained, and the results were analyzed and discussed. The results show that average mass extinction coefficient has a decrease of 4.6 percent in the 3-5 um waveband and a decrease of 89.5 percent in the 8-14 um waveband. In light of this, to retain activity of aspergillus niger spores will play an important role in the increasing of its electromagnetic attenuation abilities.