Water sorption into polylactide (PLA) and polylactide-montmorillonite (PLLA-MONT) composites containing 5 wt % of montmorillonite (MONT) under different heat treatment conditions was studied using the quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) technique. Results showed that water sorption in neat polymer films and composite films increased with heat treatment temperature up to 120 degrees C. Differential scanning calorimetry was used to measure the glass-transition temperature and isothermal crystallization kinetics of all samples. The mobility of the amorphous domain in all samples increased with heat treatment temperature, indicated by the decrease in glass-transition temperature. PLA composites crystallized at a much faster rate than neat PLA did because MONT acted as a nucleating agent. Under the same heat treatment condition, water sorption in PLLA-MONT composites was always higher than that in neat PLA due to the presence of the hydrophilic hydroxyl groups on the surface of MONT particles. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 873-881, 2011