The far-infrared reflectance spectra and the infrared detection characteristics of the new infrared material of InN0.01Sb0.99 thin films were reported. Far-infrared reflectance spectra, blackbody photoresponses and photocurrent spectra of the lattice mismatched InN0.01Sb0.99 film on GaAs substrate have been measured. A prototype wide-band infrared detector whose response peak at 4.4 μm and cut-off wavelength at 5.7 μm with the FWHM of 3.5 μm has been obtained. By investigating the annealing effects on the device performance, it is found that the crystal quality and the response capability are improved and the Moss-Burstein effect is reduced after annealing.