This work was aimed to develop water resistant biocide film from renewable resources for applications in food and water technology. Guar gum, a polymeric galactomannan, was intrinsically modified to a new guar gum benzamide. Benzoylation was carried out by benzoyl chloride reaction in water medium and a propyl amine spacer was used to impart a high degree of hydrophobicity. The new guar gum benzamide was resistant to water and soluble in non aqueous solvent like dimethyl sulfoxide. Cast films of thickness 0.162 mm had a breaking point tensile strength of 21.95 Mpa. The water vapor permeability of biomaterial film was 0.28 g mm kPa(-1) h(-1) m(-2) and water contact angle on evaporative surface was 90.35 degree. Qualitative and quantitative biocide activity of film was established against Salmonella enterica, Escherichia coli, Staphylococcus aureus and Bacillus subtilis. The new guar gum benzamide absorbed strongly in UV region. (C) 2011 Elsevier Ltd. All rights reserved.