Nanocellulose satisfies the emerging demand for environmentally-friendly and sustainable nanomaterials. Due to the excellent material properties, such as high Young’s modulus, high strength and low thermal expansion coefficient, nanocellulose has been attracting attention as a future nanofiller in polymer nanocomposite materials. However, in development of the nanocomposites, incompatibility with hydrophobic polymers often become critical issue. Generally, to achieve homogeneous distribution of nanocellulose in hydrophobic polymer matrices, melt compounding at high temperatures or solution casting using organic solvents are necessary. In other words, to overcome the high interfacial energy between them, the nanocomposite preparation requires a lot of energy and careful processing, which hinder the commercial viability. Here, we report on a facile method to prepare nanostructured nanocellulose/hydrophobic polymer composite, through aqueous polymerization process. Surface-carboxylated nanocellulose with a width of ~3 nm was prepared by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-mediated oxidation of wood cellulose. The nanocellulose/polymer composite was successfully prepared by polymerizing the monomer encapsulated in the emulsion, with the assistance of the nanocellulose as a stabilizer. In this study, we demonstrate that the ultrafine nanocellulose can construct organized polymer nanoparticle/nanocellulose structure, and act as reinforcing nanofiller in the resulting composite materials.