In order to study the response of two cultivars of sunflower (Sakha-53 and Giza-102) to inoculation with phosphate dissolving bacteria (phosphorine) and biological nitrogen fixation bacteria (Cerealin) under different nitrogen fertilizer levels i.e. (15, 25 and 35 kg N /fad.). The main finds could be summarized as fallows: Two field experiments were conducted at Agricultural experimental farmof AL –AzharUniv. at Assiut, during 2012 and 2013 seasons.         The results revealed that sunflower cultivars exhibited significant differences in all studied traits except No. of seeds per plant. Plants of Sakha-53 were surpassed significantly Giza-102 in all studied traits in the two growing seasons.          Increasing nitrogen fertilizer levels up to 35 kg N /fad significant increased all traits under study except seed oil percentage was decreased with increasing N levels up to 35 kg N /fad in both seasons.           Results indicated that the inoculation of sunflower seed with phosphate dissolving bacteria (phosphorine) or with N₂- fixation bacteria (Cerealin) enhanced significantly all studied traits over the control except seed oil percentage in both seasons. Seed inoculation with cerealin gave highest means of all studied traits.           The interaction between cultivars and nitrogen fertilizer rates had a significantly effected plant height and seed yield ton/fad. in both seasons as wall as stem diameter and oil yield kg/fad in the first season only and seed oil percentage in the second season. The interaction between cultivars and bio-fertilizer significantly affected stem diameter, seed and oil yields /fad in both seasons, plant height and head diameter in the first season only and seed oil percentage in the second only. The interaction between nitrogen fertilizer rates x bio-fertilizer significantly affected stem diameter, number of seed per head, seed weight per head and seed yield ton/fad. in two growing seasons and plant height, head diameter and oil yield ton/fad. in the first season and seed oil percentage in the second season only.         In general it could be concluded that highest seed and oil yield/ fad was obtained from Sakha-53 cultivar when received 35 kg N /fad. and  inoculation with cerealin under Assiut conditions.