We demonstrate that increasing PHB content decreases the complex viscosity and elastic/viscous moduli in composites containing 0 and 10 wt% wood flour. However, for 20 and 30 wt% wood flour, complex viscosity increases with higher PHB content due to effects of wetting, phase separation, and strong filler interactions. The viscous modulus dominates over the storage modulus in most samples; the exceptions being PLA/PHB- 80/20 and 70/30 composites containing 30 wt% wood flour, in which the elastic modulus dominates due to formation of filler networks. Additionally, the linear viscoelastic region shifts to lower values at increased wood flour loadings, suggesting that fillers increase sensitivity to deformation. Finally, we examine the role of particle size and aspect ratio through analysis of composites containing wood fiber in place of wood flour. By relating melt rheology data to that obtained from DSC, TGA, and tensile testing experiments, we can better design bio-based polymer composites for enhanced properties and processability.