We succeeded in fabrication of monodispersed diarylethene nanoparticles using the reprecipitation method and controlling nanoparticle size in the range of 40 nm to 250 nm by changing concentration of the injected solution and viscosity of good solvent. The obtained nanoparticles exhibited photochromism by alternate irradiation of UV and visible light. In addition, the red-shift of characteristic peak position (around lambda = 570 nm) of closed-DAE nanoparticles was observed with increasing nanoparticle size, which was attributable to the strained molecular structure.