Poly-lactic acid (PLA) has been widely applied in the medical field (in biomedicines such as medical capsules, surgical sutures and suture wounds) owing to its high biodegradability, good biocompatibility and ability to be dissolved in common solvents. Chitosan (CS) is an abundant polysaccharide and a cationic polyelectrolyte present in nature. In this study, the combination of PLA and CS has been used to form PLA/CS nanocomposites having the advantages of both the original components. To enhance the dispersibility and compatibility between PLA and CS in the PLA/CS nanocomposites, polycaprolactone (PCL) is added as a compatibilizer. The Fourier Transform Infrared spectroscopies prove the existence of the interactions of PCL with PLA and CS. A more regular dispersion of CS of 200-400 nm particle size, is observed in the PLA matrix of the PLA/CS nanocomposites containing PCL, through the Field Emission Scanning Electron Microscopy images. The appearance of one glass transition temperature (T(g)) value of PLA/CS/PCL nanocomposites occuring between the T(g) values of PLA and CS in DSC diagrams confirms the improvement in the compatibility between PLA and CS, due to the presence of PCL. The TGA result shows that PCL plays an important role in enhancing the thermal stability of PLA/CS/PCL nanocomposites. The hydrolysis of PLA/CS/PCL nanocomposites in alkaline and phosphate buffer solutions was investigated. The obtained results show that the PLA/CS/PCL nanocomposites have slower hydrolysis ability than the PLA/CS composites.