Nanocomposite films were prepared by impregnating cellulose nanofiber (CNF) sheets of various chemical compositions, i.e., lignocellulose nanofiber (LCNF), holocellulose nanofiber (HCNF), and bleached kraft pulp-based nanofiber (BKP-NF), with UV-curable resin. The effects of the CNF sheet porosity on the amount of impregnated resin and the tensile properties of the corresponding nanocomposite films were investigated. The defibration efficiency, viscosity, and filtration time of HCNF and BKP-NF were higher than those of LCNF, and these properties increased with defibration time for BKP-NF. The density and porosity of the LCNF sheets were lower and higher, respectively, than those of the HCNF and BKP-NF sheets. The porosity of the CNF sheets was successfully regulated using organic solvents with different polarities. The impregnated resin amount increased as the CNF sheet porosity and the ratio of monomer to oligomer in the resin increased. The tensile strengths and elastic moduli of all of the nanocomposite films were higher than those of the neat resin films. The specific tensile strength of the nanocomposite decreased with increasing impregnated resin content.