The in vitro degradation characteristic of the poly D, L-lactic acid ( PDLLA ) / hydroxyapatite( HA ) compound fibers were investigated. The compound fibers were immersed in static phosphate buffer at 37℃to degrade for 22 weeks. The changes in pH value of the buffer solution, the mechanical strength and morphological of inside and outside of composite fibers with degradation characteristic were observed. Results show that pH value of the buffer solution stabilized to about 7.0 before 12 weeks, however after 20 weeks that pH value quick declined. After 7 weeks that composite fibers of mechanical strength cannot mensuration. SEM observation revealed that bimodal degradation occurred in composite fibers.