The present investigation was carried out to study the effect of the application of polyphenolic compounds i.e. Pyrogallic, P.coumaric acid and Tanic acid, at concentrations of 50 and 100 ppm of each, on the development of the cotton variety Giza 81. The application of the studied compounds had no significant in­fluence on growth characters in both seasons, except number and le­ngth of internodes in 1990 season, where the maximum of both charac­ters was obtained when the plants were treated with Tanic acid (50 ppm) and Pyrogallic acid (100 ppm), respectively. The compounds in­creased number of open bolls/plant, seed cotton yield per plant and per feddan, while the other characters were not clearly affected. The high­est values were obtained from the application of P.coumaric acid when applied at 50 ppm in both seasons. Treated plants were earlier in maturi­ty. Micronaire and Pressley index were not affected. The foliar spray of the compounds increased auxin content, ratio of poly to total phenols in leaves and seed protein content, while seed oil content was not affect-