In this paper, we report for the first time that metal oxide nanocrystals (MONs) including magnetic Fe3O4 and luminescent ZnO nanocrystals can be facilely synthesized through a one-step reaction by using castor oil (CO) as both stabilizer and reaction solvent. The obtained MONs with relatively uniform size (2-5 nm) show high solution dispersibility and stability. The existence of CO components on the surfaces of MONs was confirmed by thermogravimetric analysis and FTIR characterizations. Benefiting from the presence of CO components, the MONs possess multiple surface hydroxyl groups that can be easily tailored. Moreover, the MONs exhibit favorable compatibility with polymer (e.g., poly(ethylene-co-vinyl acetate)) and can not only endow the polymer with magnetic or luminescent properties but also enhance the UV-shielding and mechanical properties of polymer. Considering the simple synthetic process and robust performance of the MONs, this study may open up new opportunities for the practical applications of MONs. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.