Syntheses of diluted magnetic semiconductor Cd1-yMnyS nanoparticles varying in size from 1.9 to 3.5 nm and composition, y, from 0 to 0.3 have been performed in reverse micelles. Size and composition, y, of the particles are controlled independently. The particles are characterized by TEM, EDS, and EPR. Manganese ions rue substituted randomly in the CdS matrix. Optical absorption studies shaw, at fixed composition, a quantum size effect. At fixed size a nonlinear variation of the band gap versus composition is observed. This effect already observed in the bulk phase is more pronounced with quantum dots.