Effects of bio-degradation on the mechanical properties of polylactic acid (PLA)/hydroxyapatite (HA) were evaluated using a newly designed three-point bending fixture in SBF chamber. The composite was found to be ductile and insensitive to cracks, which is totally different from its brittle behavior observed in conventional tests, in which the degraded samples are tested in air at room temperature. Initial bending modulus and strength of PLA/HA composite were 1.2 GPa and 43 MPa, respectively, which were lower than those tested under room conditions. After two weeks of immersion in vitro, both bending modulus and strength decreased by 40% and 57%, respectively. Their degradation rates were both higher than those in reports of previous researches. This work indicates the importance of evaluating mechanical behavior in simulated body environment.