Experimental results are reported about the surface nitridation of molyly denum by repeated pulsed laser irradiation on molyboenum foils in pure nitrogen atmosphere. In this laser treatment, the laser irradiation activates nitrogen and melts Mo surface, initating a nitridation reaction in liquid phase. The obtained nitride layers were analyzed and characterized by scanning electron micrography, Auger electron spectroscopy and X -ray diffraction. It is found that the nitride layers contain γ-Mo2N phase and have microstructure much denser than that of the original material. Surface heating and melting and transient shock waves induced by laser pulses could account for the microstructure densification of the nitride layers.