The work aims to research the biodegradability of P(3HB-co-4HB)/PBS blends in the lipase solution. P(3HB-co-4HB)/PBS blends were placed in the lipase solution for experiments on enzymolysis. Biodegradability of the blends was analyzed by means of weight loss rate, scanning electron microscopy (SEM), X-ray diffraction (X-RD) and polarizing microscope (POM). The weight loss rate and SEM analysis showed that the lipase degradation effect on P(3HB-co-4HB) was not obvious, while such effect on PBS was more significant. XRD analysis showed that the intensity of the blends’ crystal diffraction peak at 19.9° and 22.7° decreased with the enzymolysis time, which indicated that the main degraded component was PBS. The POM results showed that the spherulite morphology of P(3HB-co-4HB) before and after enzymolysis was basically unchanged. The enzymic hydrolysis of PBS ester bond is relatively easy, while the hydrolysis of P(3HB-co-4HB) ester bond is difficult. PBS is preferentially degraded in the P(3HB-co-4HB)/PBS blends in the lipase solution. Moreover, there is no selectivity on the crystal area and amorphous area of materials during enzymatic degradation of lipase.