In a previous work [Macromolecules 1998, 31, 6426] the preparation technique of a latex of poly(beta-hydroxyoctanoate) (PHO) obtained from Pseudomonas oleovorans grown at high cell density on sodium octanoate was presented. The resulting films displayed typical properties of thermoplastic elastomer. Depending on the experimental purification conditions, fully amorphous PHO films can be obtained. Nanocomposite materials were prepared using this latex as a matrix and using a colloidal suspension of hydrolyzed starch or cellulose whiskers as a natural and biodegradable filler. After stirring, the preparations were either cast and evaporated or freeze-dried and molded. High-performance materials were obtained from these systems, preserving the natural character of PHO. The resulting properties were strongly related to the aspect ratio L/d (L being the length and d the diameter) of the filler and to the geometric and mechanical percolation effects. In addition, specific polymer-filler interactions and geometrical constraint due to the particle size of the latex have to be considered to account for the mechanical reinforcement effect of cellulose whiskers.