A degradable L-PLA/calcium carbonate composite made of interconnecting phases was examined. This structure was used both to slow the degradation rate and to reduce the brittleness of the ceramic. Both in vitro and in vivo degradation studies were performed. Samples were incubated in buffered saline or placed in the dorsum of rats for 0, 1, or 4 weeks. Mechanical testing was performed on both groups, volume fraction of each component was determined for in vitro samples, and histology was performed on in vivo samples. Failure load, tensile strength, and elastic modulus significantly decreased during the 1st week for both groups. Continued decreases were seen at 4 weeks for in vitro samples but not for in vivo. Failure strain and tensile strength decreased only for in vitro specimens. PLA fraction significantly decreased during the 1st week and then stabilized. Histology showed that tissue ingrowth occurred at 4 weeks. The decrease in mechanical properties was probably a result of the decreased PLA fraction. The stabilization and even a slight increase in tensile strength and failure strain in the in vivo samples was probably due to the tissue ingrowth forming an implant-tissue composite.