Nanocrystalline (RNH3)2PbI(4)-doped PMMA films were successfully fabricated on glass substrates by the spin-coating technique and subsequent annealing. X-ray diffraction spectra revealed that the (RNH3)(2)PbI4 crystals dispersed as nanometre-sized crystals in the PMMA matrix. These films showed a strong exciton absorption band with narrow bandwidth, even at room temperature. The exciton absorption observed here could be attributed to the 6s to 6p transition of Pb2+. The stability of the (RNH3)(2)PbI4 crystal was improved by doping these crystals into a PMMA matrix.