Two novel bacterial strains were isolated from a paddy soil sample collected in Japan using GPM agar plates supplemented with superoxide dismutase and/or catalase. The strains were Gram-positive, catalase-positive and motile, with lysine as the peptidoglycan diagnostic diamino acid and acetyl as the peptidoglycan acyl type. The major menaquinone was MK-9(H(2)). Mycolic acids were not detected. The G+C content of the DNA was 66-68 mol%. On the basis of phenotypic analysis, 16S rRNA gene sequence comparisons and DNA-DNA hybridization data, it is proposed that these strains represent two novel species, Arthrobacter oryzae sp. nov. (type strain is KV-651(T)=NRRL B-24478(T)=NBRC 102055(T)) and Arthrobacter humicola sp. nov. (type strain is KV-653(T)=NRRL B-24479(T)=NBRC 102056(T)), respectively.