One of the main limits to the use of PLA is its extreme sensitivity to moisture. The objective of this work is to study the physical changes induced by water sorption on a commercial PLA grade. To this goal, samples of PLA having thickness of about 400μm, obtained by compression molding, were put into contact with water at 58°C. The samples were partially immersed in water in a closed and mixed vessel, so that the lower part was in contact with liquid water whereas the upper part was in contact with air with a relative humidity of 100%. The opacity of the samples, their crystallinity degree, their density and molecular weight were monitored during time. It was found that the samples became white and opaque after a few hours, crystallinity reached an equilibrium value after about 48h. Density was found to decrease with time, thus suggesting that the whitening was due to crazing. Surprisingly, it was found that the mentioned phenomena are more evident for the samples immersed in water than for those surrounded by a 100% RH atmosphere.