TiN and Ti_1−xAl_xN thin films with different aluminum concentrations (x = 0.35, 0.40, 0.55, 0.64 and 0.81) were synthesized by reactive magnetron co-sputtering technique. The structure, surface morphology and optical properties were examined using Grazing Incidence X-ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry, respectively. The structure of the films were found to be of rocksalt type (NaCl) for x = 0.0–0.64 and X-ray amorphous for x = 0.81. AFM topographies show continuous mound like structure for the films of x between 0.0 and 0.64, whereas the film with x = 0.81 showed smooth surface with fine grains. Micro-Raman spectroscopic studies indicate structural phase separation of AlN from TiAlN matrix for x > 0.40. Ti_1−xAl_xN has the tendency for decomposition with the increase of Al concentration whereas c-TiN and hcp-AlN are stable mostly. The optical studies carried out by spectroscopic ellipsometry measurements showed a change from metallic to insulating behavior with the increase in x. These films are found to be an insulator beyond x = 0.81.