Abstract: Four greenhouse experiments to assess the response of two physiologically different cereal crops, i.e. sorghum and rice crops representing C4 and C3 plants as well as Azospirillum spp. populations in their rhizosphere and root surface soil to inoculation with A. lipoferum in combination with five levels of N fertilizer were conducted. The results indicated that sorghum was more responsive to inoculation than rice plant. Maximum benefits were obtained when the N fertilizer level was reduced to 30 kg/fed. in combination with A. lipoferum inoculant, giving the superiority in yields and yields components of both plants. There was a moderate difference of the rhizosphere and root surface soil effect on Azospirillum spp. population density between the two different groups of plants. However, MPN of Azospirillum spp. surrounded the root system of C4 plant recorded greater value than that of C3 one.