The inhibition of Aspergillus niger that causes root rot diseases in peanut (Arachis hypogaea L.) was investigated by using 765 bradyrhizobial and 350 soil-isolated plant growth promoting rhizobacteria (PGPR) strains as biological controllers. Only 11 PGPR isolates were found to be able to inhibit A. niger growth. Based on their ability to inhibit A. niger growth and root colonization, the best four PGPR isolates, A20, A45, A62, and A106, were selected, and their 16S rRNA sequences were highly homologous to Bacillus megaterium, B. subtilis, B. subtilis subsp. subtilis, and Pseudomonas sp., respectively. The production of a lytic protease enzyme was detected in A20, A45, and A62, but not in A106. Some antifungal activities were clearly found in cell-free supernatants of A20 and A62. Interestingly, the antifungal activity of isolates A45 and A62 was proteinase K resistant. All PGPR isolates could produce an auxin (indole-3-acetic acid, IAA) hormone and biofilms. IAA produced from PGPR isolates could clearly promote peanut root growth. When either isolate A20 or A45 (10 8cellsper ml) was co-inoculated with Bradyrhizobium sp. TAL 173 (10 8cells per ml), the peanut root rot disease caused by A. niger (10 5 and 10 6spores per seed) could be inhibited. Incorporating rhizobia with selected PGPR increases nitrogen fixation and reduces fungicide usage in peanut, providing an appropriate approach for sustainable agriculture. © 2012 Elsevier Inc.