Fluorescence behavior of nanoparticles of several aromatic compounds was studied. Doped nanoparticles were also studied. Transparent organic nanoparticles dispersed in water were prepared by reprecipitation method. Addition of polyvinyl alcohol in water improved nanoparticle formation significantly. Fluorescence spectra and fluorescence quantum yields were measured by an absolute photoluminescence quantum yield measurement system. Although many organic compounds we studied hardly fluoresced in nanoparticles, fluorescence quantum yields of nanoparticles made of anthracene and its derivatives were relatively high. Doping of anthracene nanoparticles with naphthacene quenched fluorescence of anthracene nanoparticles and strong fluorescence of doped naphthacene was observed. Fluorescence quantum yield of naphthacene doped anthracene nanoparticles was as high as 0.68. Fluorescence lifetimes were also measured. Anthracene nanoparticles had shorter fluorescence lifetimes than anthracene molecules.