This study was carried out during two successive seasons of 2005/2006 and 2006/2007 on pot marigold plant (Calendula officinalis, L.) at the Experimental Station of Ornamental Plants, Fac. of Agric., Mansoura Univ., aiming to investigate the response of pot marigold plants to three rates of each of strain of nitrogen fixing bacteria “Azospirillum sp." under the commercial name of “Nitrobein", phosphate dissolving bacteria “Bacillus megaterium" under the commercial name of “Phosphorein" were applied to pot marigold seedlings after one month of sowing. The soil inoculation was repeated twice every month. While, yeast as a foliar spray at the rates 0, 1, 2 and 4 g/L. Results showed that all treatments of biofertilization improved different vegetative growth characters, promoted flowering parameters and stimulating various chemical constituents compared with control. However, it is evident that the application of active dry yeast treatments as a foliar spray proved to be the most favorable as significant increases in vegetative growth, best quality and quantity of flower production and various chemical constituents such as carotenoids, carbohydrates and oleanolic in the flower as well as chlorophylls contents and nitrogen and phosphorus percentage in the leaves. The data showed that the growth characters and chemical constituents of pot marigold plants were significantly increased when the plants received the three dry yeast applications. The highest concentration of dry yeast (4 g/L) induced significant improvement in the all growth characters and chemical composition.    Hence, these findings clearly indicate that active dry yeast could be used as effective tools instead of chemical fertilization, lowering the productive costs and consequently minimize the pollution of the agriculture environment.