InAsSb epilayers grown on GaAs substrates by molecular beam epitaxy have been studied using X-ray diffraction and Raman scattering. X-ray diffraction was used to determine the mole fraction of presented samples. In Raman spectrum, we analyzed for each sample not only the position of LO InAs and InSb phonons but also intensities of those. We found correlation between intensities ratio of LO phonons and the mole fraction of measured samples and we proposed a method how to calculate InAsSb mole fraction only using Raman spectroscopy.