The results of experiments into laser assisted gas carbonitriding of a Ti–6Al–4V alloy are reported. The temperature and thermal stress fields were simulated using finite element analysis. Microstructural changes in the laser treated region were examined using scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction. In the process, a carbon film was formed at the workpiece surface prior to laser processing and the laser scanning speed was kept constant during the process. It was found that the laser treated layer extended uniformly along the surface; the depth of the layer was about . The formation of , TiN, and TiC in the surface region enhances the hardness significantly.