Abstract: A series of experiments was carried out on the effect of gibberellin on paddy rice and winter wheat. Since 1958, 15 different experiments with more than 50 separate treatments including various concentrations and doses of gibberellins, and all the main developmental stages of the plants, besides, several varieties of rice and wheat and also, potted plants and field test in varies districts were employed in these work during the five successive years (from 1958 to 1962). The following conclusions may be made from the results of the present studies: 1. Gibberellin has a profound effect on the growth of the vegetative organs of both rice and wheat plants. At a certain developmental stage, the treatment promoted the growth of stems as well as the leaves of the plants. 2. Treatment with this hormone does not significantly affect the development of both plants the tillering time, seed weight and the total yield are not affected. As a whole, the yield of both crop plants treated with gibberellin was neither increased nor decreased under our experimental conditions. We hope that the results of our four years work may be helpful to those who are working with gibberellins, especially those dealing with the grain crops.