Abstract In this work, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was modified by cellulose derivatives, and the effects of different kinds of cellulose derivatives on the crystallization and mechanical properties of PHBV were investigated. The crystallization and mechanical properties of PHBV/cellulose derivatives composites were measured by means of differential scanning calorimeter, polarizing microscope, and mechanical properties testing instruments. Studies show that cellulose acetate (CA) can promote the crystallization of PHBV, a small amount of CA can significantly increase the crystallization temperature of PHBV. The crystallization rate of PHBV was also accelerated by CA. However, the addition of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) decreased the crystallization temperature of PHBV and inhibited the nucleation of PHBV. And the degree of inhibition increased with the increase of CAB and CAP content. CAB and CAP have good compatibility with PHBV, CAB, and CAP can be uniformly dispersed in PHBV. Cellulose derivatives with specific component content can enhance the tensile properties of PHBV without losing the impact strength.