© 2013 Elsevier B.V. All rights reserved. Undoped InAs 1-x Sb x epilayers with different compositions (0.55 ≤ × 0.78) were grown by molecular beam epitaxy on semi-insulating GaAs (1 0 0) substrates. The quality of the samples was determined by high resolution X-ray diffraction (HRXRD) rocking curves and the lattice dynamics were studied by using Raman spectroscopy at room temperature. Optical phonon frequency range shows strong two-mode phonon behavior for all compositions. With an increase in the Sb composition, InAs-like longitudinal-optical (LO), and transverse-optical (TO) phonon peaks exhibit a blue shift whereas a red-shift was observed for InSb-like LO phonon peak. Moreover, transverse-acoustic (TA) and mixed mode InSb-like 2IA/2TA phonon modes were identified successfully. HRXRD results revealed that the best full width at half maximum value reported up to now was achieved for the sample with a composition of x = 0.55 and thickness of 550 nm.