Impact strength of a modified cardanol-bonded cellulose thermoplastic resin was greatly improved by using a small amount of olefin resins. As we showed, this thermoplastic resin (3-pentadecylphenoxy acetic acid (PAA)-bonded cellulose diacetate (CDA): PAA-bonded CDA) exhibited high practical properties such as bending strength, heat resistance, and water resistance. However, its impact strength was insufficient for use in durable products. We improved the impact strength of PAA-bonded CDA by adding hydrophobic olefin resins, such as polyethylene or polypropylene, while maintaining good bending strength and breaking strain. Furthermore, the application of olefin resins also increased water resistance and fluidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39829.