Injection-molded bamboo fiber/PBS (polybutylene succinate) composites were studied; especially much attention was focused on their fracture behavior. The effects of filling rate and size of the bamboo fiber (BF) to the resin on fractural behavior were evaluated by tensile and Izod impact tests. The tensile strength of the composites of BF particle size the range from +75 to -180 m and from +180 to -250 m were higher than those of -75 m and those of +250 to -500 m. However, there are many pull-out fibers on fracture surface. The surface of the fiber had no sticking of PBS resin. The impact strength of the composites increased with increasing BF content except for the case that BF particle size was -75 m. After impact tests, in the case of the composites prepared using large BF, the fractural surfaces became bumpy. The changes in shapes of the composites derived from immersion in boiling distilled water were examined by using a digital microscope. After immersion in the hot water, many cracks appeared on the outer surface of the composites. These cracks might be responsible for the brittle fracture behavior of the water-absorbed composites.