Poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) are two kinds of biocompatible and biodegradable materials that have been widely employed in the industrial and medical field. Even though PLLA exhibits relatively good mechanical properties, its commercial products are limited by its brittleness and stiffness. PCL exhibits a significant drug permeability and elasticity but very low degradation rates due to the relavitely high crystallinity. Therefore, copolymerization of PLLA with PCL could allow the fabrication of a variety of biodegradable materials with improved properties in comparison with those of the parent homopolymers. During the last several decades, researches have been focoused on the crystallization behavior of pure PCL and PLLA. However, the crystallization behavior and morphology of PCL-PLLA copolymer films have seldom been a concern. As well known, the crystallization temperature and molecular weight are the important variables governing the crystallization behavior of polymers, and the crystalline morphology may significantly change at the microscopic and nanoscale levels. Thus, discussion and investigations on the effect of crystallization temperature and molecular weight on crystallization behavior and morphologies would also provide useful information for future application of the PCL-PLLA block. In this study, the crystallization behavior and morphology of diblock copolymers PCL-PLLA with different ratios of the chain length of the two blocks is investigated with polarized optical microscope, atomic force microscopy, scanning electronic microscopy and differential scanning calorimetry. Detail discussion on the crystallization morphology of PLLA-PCL diblock were also performed. The effect of molecular weight and temperature programming on the crystallization behavior and crystal morphology of PCL-PLLA diblock copolymers has been studied.