In this paper, we present, for the first time, the magnetic properties of Cd1-yMnyS nanocrystals of average size (4 nm) at various compositions, y. We demonstrate that the Mn-Mn interactions are markedly enhanced compared to the bulk material. As in the bulk phase, the photuluminescence and the EPR hyperfine structure, both attributed to isolated Mn2+ ions in a tetrahedral coordination, behave similarly with increasing composition. At the opposite of the bulk phase, isolated Mn2+ ions are observed for a rather large composition (y = 0.08) in nanocrystals. We attempt to relate the change of the band gap with composition with the various manganese interactions.