Laser gas assisted nitriding improves the properties of steel surfaces through grain refinement and nitride compounds formation in the surface region. In the present study, laser gas assisted nitriding of tool steel (H13) is carried out. The microstructural and morphological changes in the laser nitrided region are examined using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The first and second law efficiencies of the laser nitriding process are formulated using the lump parameter analysis. It is found that the depth of nitride layer extends 60 mu m below the surface. The nitrided layer is free from cracks and voids. The first and second law efficiencies reduce with increasing laser power; however, they increase significantly with increasing laser scanning speed.