Samarium hydroxide (Sm(OH)(3)) is an important samarium compound with many potential applications in electronics, optics and catalysis. Based on a facile hydrothermal method assisted by oleic acid surface modifications we synthesized Sm(OH)(3) nanocrystals with various morphologies. In this system, by adding the oleic acid surfactant both crystallization and grain size of nanocrystals can be tuned. Furthermore, the paramagnetic resonance and magnetic measurements point out that rod-like Sm(OH)(3) samples are non-magnetic, while Sm(OH)(3) disc-like samples exhibit weak ferromagnetism. The correlation between magnetism and morphology in Sm(OH)(3) nanocrystals is associated with the surfactant-induced surface modification as well as with the changes in the localization of electrons in Sm 5d orbitals, in agreement with X-ray absorption spectroscopy data.