The effects of the short-term application of Ascophyllum nodosum-fermented seaweed fertilizer on the bacterial community, soil nitrogen contents, and plant growth in maize rhizosphere soil were evaluated. The changes in the bacterial community composition and nitrogen contents including those of total nitrogen (TN), nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N) in rhizosphere soils in response to treatment with seaweed fertilizer were determined. Furthermore, soil enzymatic activity and crop biomass were analyzed. The relative abundance of the dominant phyla varied regularly with fertilization, and bacterial α-diversity was apparently influenced by seaweed fertilizer amendment. The TN contents of all soil samples decreased gradually, and the NO3--N and NH4+-N contents of the soils treated with seaweed fertilizer were much higher than those of the control soils. Similarly, the enzymatic activities of dehydrogenase, nitrite reductase, urease, and cellulase in the soil were significantly increased on day 3, day 8, and day 13 after the application of seaweed fertilizer to the maize rhizosphere soil. However, there was no difference in the activity of soil sucrase between the treatment group and the control group. In this study, the growth of maize seedlings was confirmed to be greatly promoted by the utilization of seaweed fertilizer. These results deepen our understanding of plant-microbe interactions in agroecosystems and should benefit the wide use of seaweed fertilizer in sustainable agricultural production.