We screened a mini-Tn10 insertional mutant library of the spore-forming bacterium Paenibacillus polymyxa E681 with variable indole-3-acetic acid (IAA) productivity. Four mutants, of which two showed a decrease in IAA production and the other two showed an increase in IAA production, were finally selected. Further analyses demonstrated different levels of IAA intermediates from culture supernatant of wild-type strain and mutants. In addition, mutants showed different promotions on the early growth of 10-day-old maize in terms of the increase in shoot and root weights. DNA fragments flanking the transposon insertion in four mutants were cloned and sequenced. The target sites of insertion were gene gpr1, disrupted at two sites, 49 bp downstream of the spo0F gene, and relA/spoT homologue, which codes for GPR1/FUN34/YaaH family protein, stage 0 sporulation protein F, and RelA/SpoT domain protein, respectively. This evidence suggests that there may be a number of genes involved in the regulation of IAA biosynthesis of P. polymyxa.