Abstract A method of width gauging of surface slot using laser-generated Rayleigh waves in time domain is presented. A two-step detection is employed in this method, Rayleigh waves are first generated on one side of the surface slot and then on the other side. Incident and reflected Rayleigh waves from surface slot are detected respectively on both sides of the slot in the two detections. Width of surface slot is calculated based on the arrival time of incident and reflected Rayleigh waves. Experiment results agree well with the measured results by digital microscope and validate the feasibility of the proposed method. The approach will open the way for simultaneous measurement of the depth and width of surface slot and provide a potential application for characterization of surface slot in extreme environment and width gauging of subsurface structure.