A microfluidic device was designed and fabricated for non-photochemical laser-induced nucleation (NPLIN) in continuous laminar flow, which enabled real-time in situ characterization of crystal size, shape, growth, and polydispersity. On-chip thermoelectric cooling created supersaturation by lowering the solution temperature. The influences of laser power density, laser exposure time, flow rate, and supersaturation were examined for aqueous KCl solutions. The observed threshold peak power densities and solution labilities agreed with those reported by Alexander et al. using static cells. The mean crystal size just downstream from the irradiated region was observed to increase with increasing supersaturation. The number of crystals nucleated was found to increase with increasing supersaturation and laser power density but was independent of the number of laser pulses to which the solution was exposed. These results are consistent with the dielectric polarization model of Alexander et al. Our findings broaden the scope of nucleation in a light field by introducing a way to directly characterize the crystallization.