The purposes of this article are to synthesize the biomass-based hybrid nanocomposites using green method in green solvent and evaluate its biological activity. In this paper, microwave-assisted ionic liquid method is applied to the preparation of cellulose/CaCO 3 hybrid nanocomposites in the alkali extraction cellulose using CaCl 2 and Na 2 CO 3 as starting reactants. The ionic liquid acts as the excellent solvent for absorbing microwave and the dissolution of cellulose, and the synthesis of cellulose/CaCO 3 nanocomposites. The influences of reaction parameters such as the cellulose concentration and the types of solvent on the products were investigated. The increasing cellulose concentration favored the growth of CaCO 3 . The morphologies of CaCO 3 changed from polyhedral to cube to particle with increasing cellulose concentration. Moreover, the solvents had an effect on the shape and dispersion of CaCO 3 . Cytotoxicity experiments demonstrated that the cellulose/CaCO 3 nanocomposites had good biocompatibility and could be a candidate for the biomedical applications.