The effects of microbial transglutaminase (MTGase) treatment at various enzyme concentrations (4-40 U g(-1)) on the properties of cast films from red bean protein isolate were investigated. The evaluated properties included mechanical properties (tensile strength, TS and elongation at break, EB), surface hydrophobicity (H(s)), moisture content (MC), total soluble matter (TSM), water vapor transmission rate (WVTR) and permeability (WVP), as well as transparency. The results indicated that the TS and EB, and TSM were greatly improved by the MTGase treatment at low enzyme concentrations of 4-10 U g(-1), but considerably impaired at higher concentrations 20-40 U g(-1). The MTGase treatment also significantly increased the H(s), but decreased MC and WVTR, but the changes were independent of the applied enzyme concentration. The MTGase treatment progressively decreased the moisture loss during the drying of film-forming solutions, upon the increase in enzyme concentration. The protein solubility analyses in various solvents indicated that the contribution of covalent linkages to film network formation progressively increased upon the increase in enzyme concentration. The results suggest that the modifications of the properties of cast films are closely associated with the extent of MTGase-induced covalent polymerization and/or aggregation. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 789-797, 2011