Chemically modified cellulose nanocrystals (CNCs) were synthesized by grafting poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) onto CNCs via homogeneous acylation reaction between N,N-dimethyl formamide (DMF) by using toluene diisocyanate (TDI) as coupling agent and dibutyltin dilaurate as catalyst. The resulting copolymers were studied by using (1)HNMR, FT-IR, WAXD, DSC, TGA and contact angle measurements. Results showed that the copolymers kept their initial morphological integrity. Moreover, it is found that with the increase of the TDI/PHBV fractions, two transition exhibitions occurred in their thermal and hydrophobic properties, which could be modulated through controlling the lengths and grafting densities of PHBV side chains. Compared with those of neat PHBV, the crystallization of PHCN7 became easy while the crystallinity slightly decreased to 55.5%, the maximum decomposition temperature increased by 48.5°C, meanwhile the contact angle increased to 58° as compared to neat CNCs (30°).