The present invention relates to an apparatus and method for measuring the size of nanoparticles present in an aqueous solution as an infinitesimal quantity, and, more particularly, to a scheme that remotely measures the laser-induced breakdown of a fine nanoparticle using a probe beam in a non-contact manner, performs curve fitting on the symmetrical frequency distribution curve of the measured magnitude of a probe beam signal to form the shape of a Gaussian function, obtains calibration curves for the size of the nanoparticle from the peak and full-width at half-maximum thereof, and determines the size of an unknown nanoparticle from the calibration curves.