In the present study, carbon fiber-reinforced polylactide (C/PLA) composites with different interfacial conditions were prepared to determine the influence of interfacial adhesion strength (IAS) on in vitro degradation behavior of the C/PLA composites. Pure PLA and untreated and treated C/PLA composite samples were immersed in phosphate buffered saline (PBS; pH 7.4, 37 +/- 0.5 degreesC) for predetermined time periods. These samples were removed at each degradation time, measured to analyze molecular weight loss, weighed to assess water uptake and mass loss, and mechanically tested to obtain bending strength, modulus, and IAS. The matrixes in the C/PLA composites showed higher water uptake and lower mass loss in comparison with the pure PLA. Further, the PLA matrix in the treated composite absorbed less water and lost less mass and molecular weight than its counterpart in the untreated composite. Mechanical tests confirmed that the treated C/PLA composite exhibited a slower rate of decrease in bending strength, modulus, and IAS than the untreated one. The differences in degradation behavior between two composites can only be attributed to the difference in interfacial conditions because all other parameters were kept constant. The loss of bending strength and modulus was mainly caused by the interface degradation of the C/PLA composites. It can be concluded from our in vitro observations that the IAS had an obvious influence on the degradation characteristics of the C/PLA composites.