Polylactide (PLA (3251D))/ Cellulose nanocrystal (CNC) and poly [(butylene adipate)-co-terephthalate] (PBAT)/CNC nanocomposites and PLA/PBAT/CNC blend nanocomposites were prepared through a solvent casting method. Two solvents were used to disperse CNCs and dissolve PLA, PBAT and their blends. Atomic force microscopy showed a very good dispersion of CNCs in both polymers and their blends. The complex viscosity and storage modulus of polymers and their blend nanocomposites were increased. The crystallization temperature and total crystalline content of PLA, and PBAT nanocomposites were increased, which is an indication of the nucleation effect of CNCs on the crystallization of PLA and PBAT. The Young modulus of the nanocomposites increased with the CNC content. On the other hand, the yield strength and elongation at break of neat polymers and their blends decreased. In dynamic mechanical analysis (DMA), the storage modulus of the nanocomposites steadily increased with the incorporation of CNCs. The storage modulus at room temperature and at 70 C is described by a recently proposed percolation model that explains the improvement of thermal properties of the PLA and PLA/PBAT nanocomposites compared to the neat PLAs.