Cellulose fibers, cell wall fragments and cellulose microfibrils can be used as reinforced materials for biocomposite manufacture. Understanding nano-mechanical properties of those materials will be very useful to show their full theoretical potential. Nanoindentation testing is a technique that determines the mechanical properties of a material in the sub-micron/nano scale. The test involves penetrating a sample material using an indenter, while the penetration depth and load are recorded so that the stiffness and hardness of the indented location can be subsequently calculated. The objective of this study was to understand the mechanical properties of wood cell wall, regenerated cellulose fiber and cellulose fiber-reinforced polypropylene composite using nanoindentation. The effect of microfibril angle on the hardness and stiffness values of wood cell wall and the mechanical properties of interphase between regenerated cellulose fiber and polypropylene were investigated. Time dependent mechanical properties of regenerated cellulose fiber in longitudinal and transverse direction were also investigated.