In this paper, Ag@Fe 3 O 4 @cellulose nanocrystals (CNC) nanocomposites were synthesized by a facile and green microwave-assisted hydrothermal method. In the procedure, CNC was used as a reducing agent for the synthesis of Ag. During the whole synthesis process, there were no additional reducing agents or toxic solvents used. The nanocomposites were characterized by X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectrum, transmission electron microscopy, thermogravimetric analysis, and differential thermal analysis. In addition, Ag@Fe 3 O 4 @CNC nanocomposites were also synthesized by microwave-assisted method and hydrothermal method. Both the effects of reaction time and synthetic procedures on the reduction process of Ag + by CNC were explored. The results showed that Fe 3 O 4 was formed with sphere-like structure and dispersed uniformly. Ag@Fe 3 O 4 @CNC nanocomposites exhibited good adsorption of dye solution, which showed potential applications in water treatment. The antibacterial results showed that Ag@ Fe 3 O 4 @CNC nanocomposites had good antibacterial activities toward both Staphylococcus aureus ( S. aureus ) and Escherichia coli ( E. coli ). The green and facile strategy reported in this paper may be broadly used in synthesizing other metal nanoparticles, as well as organic–inorganic nanocomposites.