Abstract: In a method for estimating nanoparticles in a solution, a laser-induced plasma is generated by making a pulsed laser beam incident on inside a cell containing a solution, feedback signals is acquired based on light, shock wave and sound generated by the laser-induced plasma, the feedback signals, an intensity of the laser incident on the cell, and intensities of each laser passing through the cell for each laser pulse are acquired, the feedback signals acquired for each laser pulse, the intensity of the laser, and the intensities of the lasers passing through the cell into a pre-trained nanoparticle estimation model is input to estimate sizes or types of unknown nanoparticles included in the solution.