In this paper, the laser surface treatment of Fe52Cr18Mo7B16C4Nb3 alloy has been investigated with the use of pulsed Nd:YAG laser, and the optimum pulse duration parameter for having finer microstructure, highest hardness and the most homogeneous surface has been studied. Melt profile and structure of laser processed samples were investigated by use of optical and field emission scanning electron microscopes and X-ray diffraction (XRD). Moreover, the mean crystallite size of laser treated zones was studied by the Scherrer formula. Hardness of the samples was measured by means of microhardness testing device. Results showed that by decreasing the laser pulse duration and power density in the surface of the laser treated zone the highest amount of the hardness can be achieved. Moreover, peak broadening phenomenon was observable in XRD patterns of samples with lower pulse duration. It is due to the increasing of thermal gradient in the surface as a result of decreasing power density.