Simple routes to synthesize highly photoluminescent monodisperse thiol-capped CdSe nanoparticles are reported. The as-synthesized water-soluble CdSe nanoparticles possess higher photoluminescence quantum efficiency (up to 22%), smaller values of full width of half-maximum of photoluminescence spectra (down to 31 nm), higher photostability, and better monodispersity compared with the nanoparticles made from other aqueous routes. The quality of CdSe nanoparticles prepared by our route compares very favourably with those prepared in organic solution.