Biodegradable and non-toxic plastic as food packaging is used instead of conventional plastic. One of biodegradable and non-toxic plastic can be made from cassava starch and PVA. This paper reports the results of a study of the effect of glycerol content on the mechanical and water barrier properties of cassava starch/Polyvinyl alcohol (PVA) composite films. The composite films of cassava starch/PVA were prepared with a solution casting method by the addition of glycerol or not. Glycerol concentrations in composite films varied from 10, 20 and 30% by weight of the polymer in the mixture. Mechanical and water barrier properties of cassava starch/PVA were analyzed. Film transparency was analyzed using a UV-Vis spectrophotometer. Changes in the functional groups on the FTIR spectra of composite films were also observed. Tensile strength decreased with increasing glycerol concentration on composite films but increased the elongation. The addition of glycerol decreased the water barrier properties by increasing the rate of transmission of water vapor from cassava starch/PVA composite films. Film transparency increased with the addition of 10% and 20% glycerol then decreases when the addition of 30% glycerol. Mechanical and water barrier properties of the composite films indicated that the addition of glycerol modified their properties significantly.