We report on the synthesis of diluted magnetic semiconductor Cd1-xMnxS quantum dots (QDs) by the reverse micelle method using H2S as the sulfur source. The Cd1-xMnxS QDs size ranging from similar to3.2 to similar to4.2nm can be systematically controlled by the amount of H2S added and is characterized by high-resolution transmission electron microscopy. Manganese compositions in the QDs are estimated by energy dispersive spectrometry to be up to similar to3%. Electron spin resonance spectra analysis indicates that Mn2+ are incorporated into the US lattice by substituting Cd2+ sites. Optical absorption spectra of the Cd1-xMnxS QDs exhibit well-defined excitonic peaks resulting from the quantum-confinement effect. The peak position and absorption edge show systematic changes with the QDs sizes and Mn2+ compositions. (C) 2004 Elsevier B.V. All rights reserved.