Background and Objective:Bacillus pumilus strain TUAT1 is a plant growth-promoting rhizobacteria and active ingredient in commercial biofertilizers. In this study, B. pumilus TUAT1 strain was inoculated onto Arabidopsis thaliana seedlings to examine its effects on plant growth and the expression of plant hormone-related genes, growth effects were then compared between accessions. Materials and Methods: Spore suspensions of B. pumilus TUAT1 strain were inoculated at different concentrations (1×106 , 1×107 and 1×108 Colony-Forming Units (CFU) mLG1 ) into 2 weeks old seedlings of four Arabidopsis accessions (Col-0, Uk-1, Uk-3 and Bla-1). Differences between the shoot and root sizes, fresh weights and dry weights of seedlings 2 weeks after inoculation and those in non-inoculated plots were detected by t-test or analysis of variance (Tukeyʼs test). Differences in transcript levels of plant hormone-related genes were also detected in Col-0 seedlings inoculated with 107 CFU mLG1 spore suspension. Results: Treatment with 1×107 CFU mLG1 spore suspension to Col-0 seedlings significantly increased the size and weight of shoots, root weight and lateral root numbers. The same treatment also altered the transcript levels of genes related to phytohormone synthesis including NCED3, TAA1 and ACS7. The growth-promoting effects of spore treatment were also observed in accessions Bla-1 and Uk-1 but not in Uk-3. In Bla-1, root growth promotion was observed even at spore suspension concentrations of 1×106 and 1×108 CFU mLG1 . Conclusion: The inoculation effect observed in Arabidopsis was similar to that reported in rice, suggesting that the mechanism by which this bacterial strain promotes plant growth may be common to a wide range of plant species.