The growth process of selenium nanoparticles prepared in a microemulsion by a reverse micelle method is probed by several techniques. The smallest particles synthesized are of the order of 40 Angstrom, in diameter, producing the usual blue shift in the optical spectra. An amorphous to crystalline phase transition was detected by both electron and X-ray diffraction, The micelle structure investigated by small-angle neutron scattering was found to be unaffected by the conditions of the reaction.