Nanometer-sized gelatin particles have been prepared by means of gamma-ray irradiation and characterized by static and dynamic light scattering combined with circular dichroism (CD) measurements. The molecular weight of the nanoparticles was much larger than that of the original gelatin molecules, whereas the hydrodynamic radius was much smaller. Radius of gyration evaluated from the angular dependence of the static light scattering intensity decreased with increasing irradiation dose. CD spectra of the gelatin nanoparticles were independent of temperature, and it is suggested that the nanoparticles consist of highly and randomly packed gelatin and their conformation is stable against the temperature change.