<p>Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) held promise as a bio-based thermoplastic material, however, its industrial applicability was impeded by factors such as large spherulite size, brittleness, and suboptimal processability. To overcome these limitations, a bio-based engineering polyester elastomer (BEPE) was introduced and blended with PHBV, resulting in blends that were entirely bio-based. To enhance the toughness of the PHBV/BEPE blends, copper sulfate (CuSO₄) was introduced as a compatibilizer. By forming metal coordination bonds, CuSO₄ effectively improved the interfacial interaction between the two moieties of the blends, leading to improved mechanical properties. The results indicate that compared with PHBV/BEPE blends, the elongation at break of PHBV/BEPE blends containing 2.0&#xa0;phr CuSO₄ increased from 2.42 to 6.98%, and the tensile strength increased from 16.48 to 20.71&#xa0;MPa. The addition of CuSO₄ facilitated heterogeneous nucleation, resulting in a reduction in the crystallization size of PHBV. Notably, metal coordination bonds were formed between CuSO₄ and both PHBV and BEPE, while hydrogen bonding between PHBV and BEPE further strengthened their compatibility. This synergistic effect significantly improved the toughness and strength of the blends, thus greatly enhancing its feasibility and advantages in numerous industrial applications.</p>