To study the effect of inoculation with Ng-fixing bacteria on sugar beet. a green house experiment was carried out in the season of 200412005 using four nitrogen fixing bacteria to select the bacteria that sutable for oscar boly variety .Based on the results obtained from this experiment Rhizobium st. ICARDA 441 and Azolobecler chroococum were chosen for the field experiment. The field experiment was conducted at Kafr El-Sheikh Governorate season (2005l2006) using both chosen bacteria strains each individually as biofertilizer under two levels of nitrogen (45 kg N lfed and 90 kg N lied) and three levels of molybdenum (0 . 0.5 kg Mo l fed and 0.75 kg Mo lfed). Results indicated that increasing N-dose up to 90 kg led caused a significant reduction in the values of leaves dry weight , leaf N content,nitrogenase and dehydrogenase activities, this reduction was more pronounced especially in nitrogenase activity under both tested bacteria strains ,meanwhile , both bacteria strains attained significant increases in the values of leaves dry weight and N-content under the low dose of nitrogen (45 kg led). Application the low dose of nitrogen (45 kg N l fed) combined with Azolobacler inoculation produced the highest significant yields of teps, roots and sugar. Moreover. the combination between the three studied factors gave a positive significant effect on T8896 and purity 96. Rhizobla inoculation combined with the higher dose of Molybdenum (0.75 kg lied) decreased the enzyme activities and plant parameters. it could be concluded that using low dose of nitrogen (45kglfed) and low dose of molybdenum (0.5kglfed) combined with bacteria inoculation for sugar beet crop to obtain the highest yield and quality.