We investigated optical properties of colloidal solutions of nanoparticles prepared by laser ablation of quinacridonequinone powder in a poor solvent, water. Blue shift of the absorption peak energy was observed corresponding to the increase of laser fluence or to the prolonged irradiation time. For a series of colloidal solutions, we found a linear correlation between the blue shift of the absorption peak energy and the decrease in the diameter of the nanoparticles. The blue shift is considered to be due to the surface state, such as surface excitons or bond modified surface states. (C) 2012 Elsevier B.V. All rights reserved.