The response of sweet potato (Ipomoea batatas Lam.) to inoculation with Azospirillum with and without fertilizer N was evaluated in a greenhouse and field study. In the greenhouse study, storage root N concentration of ‘Centennial’ and ‘Jewel’ were higher with 34 mg N/pot + inoculant (Cd strain) than with 34 mg N/pot without inoculant. In the field study, the marketable and total root yields and root N contents of ‘Centennial’ for the 0 kg N/ha + Cd inoculant and 0 kg N/ha + TI-sp-(7 + 11) inoculant treatments were higher than for the 0 kg N/ha control and were not different from or higher than the 67 kg N/ha treatments with or without the inoculants.