Transmission and reflection measurements have been carried out on AlInN thin films. With the aid of a detailed procedure developed for analyzing the spectra, we obtained the effects of temperature on the optical properties of AlInN, such as the absorption coefficient, bandgap, Urbach bandtail characteristics, and refractive index. The absorption coefficient of the complete Urbach and intrinsic absorption regions of InN thin films has been described by a series of empirical formulas. The refractive index dispersion of AlN thin films below the band gap can be described by the Sellmeier equation. A bandtail model based on the calculation of density of occupied states and the carrier–phonon interaction has been employed to analyze the bandtail characteristics of AlInN thin films. We have also investigated Raman spectroscopy of AlInN thin films, with the emphasis on temperature dependence of phonon frequencies, which can be described well by a model taking into account the contributions of the thermal expansion of the crystal lattice, the strain between AlInN thin films and sapphire substrates, as well as threeand fourphonon coupling. These optical properties provide an experimental basis for further theoretical investigation and the design of AlInNbased devices.