In this study, we environment-friendly developed bio-based waterborne polyurethane (BWPU) through the use of both harmless water to human instead of organic solvent and natural castor oil-based polyols. Also, high crystallinity cellulose nanocrystals (CNCs) and regenerated cellulose nanoparticles (RCNs) with low crystallinity as reinforcing agents were prepared through H²SO⁴ and NaOH/urea methods, respectively. In SEM analysis, we defined that the CNC rod-like particles have a length of 100~200 nm and a width of several tens nm and that the average size of RCNs with round shape was 7~20 nm. It was shown that the crystallinity of CNCs was higher than RCNs' via FTIR and XRD analysis. In addition, it was found that as the contents of CNCs and RCNs increased, so did the properties of strength, initial modulus, and strain. It could be established that all results mentioned were constituted by the hydrogen bonding between the -OH group of nanocellulose and the -NCO group of BWPU constitutes as well as the role of nanocellulose as a chain extender. Furthermore, the maximum decomposition temperature increased with raising the content of nanocellulose. This tendency was more favorable for CNCs with higher crystallinity than RCNs with low crystallinity.