The anisotropic stresses of a-plane GaN films were in detail investigated. Nonpolar a-plane GaN films were grown on r-plane sapphire substrates by MOCVD. High resolution X-ray diffraction and polarized Raman scattering measures were performed to characterize the epitaxial films. The full width at half maximum of rocking wave is just 0.25degrees. Raman spectra provide us evidence that anisotropic stresses exist within the epitaxial GaN films. The effects of carrier gas on the stress states of the films were studied by Raman spectra. The stress was larger in film grown with hydrogen carrier gas than with nitrogen carrier gas. (C) 2003 Elsevier B.V. All rights reserved.