Abstract: Biodegradable PLLA/PHBHHx composites were prepared by means of solution blending. The effect of PHBHHx on the thermal and crystalline properties of PLLA were investigated by different scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that there existed certain misbility and interactions between PLLA and PHBHHx. The glass transtion and cold crystallization behavior of PLLA changed with the blend compositions. The larger the molecular weight of PLLA was, the worse the regularity of spherulitic morphology was. When the content of PHBHHx reached 30%, the movement of molecular segments of PLLA can be promoted. The nucleation density of PLLA crystallization can be increased and the crystallization rate can be accelerated.