The effects of succinylation at three anhydride levels (0.2, 0.4, and 0.6 g g(-1)) on the properties of cast films from red bean protein isolate (RPI) at three glycerol levels of 0.2, 0.4, and 0.6 g g(-1) were investigated. The tested properties included tensile strength (TS) and elongation at break (EB), surface hydrophobicity, moisture content (MC), total soluble matter (TSM), water vapor transmission rate, and permeability (WVTR and WVP), permeability coefficient of oil (PO). The results showed that the succinylation greatly improved the mechanical properties (especially the EB), but decreased the surface hydrophobicity of cast films. The MC, TSM, WVTR, WVP, and PO were considerably increased by the succinylation. The size exclusion chromatography analysis indicated that the succinylation resulted in protein aggregation or association, and transformation of insoluble precipitates (initially present) to soluble protein components. The dependence of the influence of succinylation upon some selected properties on the plasticizer level suggests interactions between introduced anionic succinic moieties and the hydroxyl groups of the plasticizer. These results suggest that the succinylation treatment could be applied to modify the mechanical properties of legume proteins, especially in the case that requires excellent flexibility of cast films. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1934-1941, 2011