Cd1-x MnxS diluted magnetic semiconductor (DMS) nanoparticles of crystallite size ranging from 20 to 300 A and x from 0 to 0.65 have been chemically synthesized by using aqueous solution precipitation. Subsequent characterization has been carried out by X-ray diffractometry and TEM measurements. Magnetic properties of DMS nanoparticles have been measured with a SQUID magnetometer. A transition from a para-magnetic to a spin-glass state at a critical temperature Tf has been observed. The applied magnetic field dependence of Tf has also been measured.