Cu doped CdS nanoparticles of about 2 nm diameter have been synthesized by a wet chemical method. X-ray diffraction (XRD) measurements showed that the nanoparticles have the structure of cubic phase. The broadening of XRD patterns indicate that the prepared samples are nanostructured. Transmission electron microscope (TEM) also confirms that particles are about 2nm. Room temperature photoluminescence (PL) spectrum of undoped sample only exhibited a defect related emission peak. For the doped samples, the Cu related emission peak was observed due to relaxation of carrier from excitonic states of host CdS to T-2 level of Cu. The concentration quenching was observed in our experiments. Electrical measurements made on the above samples show that electrical conductivity has strong dependence on the doping concentration, whereas it has a weak dependence on temperature.