Poly(propylene carbonate) (PPC) was melt mixed with poly(lactic acid) (PLA) and poly(butylene-adipate-terephthalate) (PBAT) in a laboratory internal mixer with a small amount of chain extender additive. Differential scanning calorimetry was used to measure their crystallization properties and crystallinity. Morphological characterization of composites was achieved by scanning electron microscopy. A comparative study of the oxygen gas barrier properties of PPC composites has been made. Tensile tests were also used to measure the mechanical properties. Results showed that there is a correlation between structure and oxygen gas barrier properties of the composites, and their structure mainly resulted from the loadings of different component of the composites and chain extender additive. Therefore, tailored oxygen gas barrier properties of the composites can be achieved.