Plasmopara viticola and Uncinula necator are the causative agents of downy mildew and powdery mildew diseases, respectively, which become a major problem in grape crop (Vitis vinifera L.). The use of natural products such as seaweed provides a rich source of structurally diverse and biologically active secondary metabolites; and is the ultimate way of combating these diseases. In this context, six different seaweed algae such as; Sargassum wightii, Padina gymospora, Caulerpa peltata, Halimeda gracilis, Acanthophora spicifera and Gracilaria opuntia; were used to control the downy and powdery mildew diseases of grapes. Enzymatic studies were carried out during two growing seasons 1 and 2 on peroxidase; polyphenol oxidase, phenylalanine ammonia lyase and β-1,3-glucanase. During season 1; in grape plants treated with Sargassum wightii, the four enzymes raised the glucose concentration to 60.79µg, 3.87µg, 5.20µg and 225.5µg; respectively, and then these plants were treated with Bordeaux mixture at 1%. After seaweed application; enzymes raised the glucose level to 59.83µg, 3.57µg, 5.17µg, 221.7µg. During season 2; when plants were treated with Sargassum wightii, the enzymes raised the glucose concentration to 62.48µg, 5.93µg, 7.25µg and 226.2µg, and then these plants were treated with Bordeaux mixture at 1%. After application; the enzymes raised the glucose level to 61.92µg, 3.57µg, 7.21µg and 224.2µg, respectively. During both seasons; β-1,3-glucanase released more amounts of glucose in both normal plants and those treated with Bordeaux mixture. The present study was undertaken to evaluate whether various extracts of seaweeds algae such as; brown, red, and green seaweeds along with the defence enzymes studied, would increase the resistance of grapes to downy and powdery mildews.