The characteristic of infrared extinction for 8 species of α and γ-nanometer aluminas was studied by dispersing in a smoke chamber and pressing potassium bromide tablet with a Fourier Transform Infrared Spectrometer. The results show that nanometer alumina possesses a good infrared extinction characteristic,and the maximum mass extinction coefficients of nanometer alumina aerosols are 1.798 m²·g^-1 and 1.940 m²·g^-1 in 3-5 μm and 8-14 μm bands. Moreover,the infrared transmission rates of γ-nanometer alumina are lower than that of α-nanometer alumina,and the infrared extinction of nanometer alumina is enhanced when the specific area increases or diameter decreases.