A novel actinomycete strain, A-T 4600(T), which developed cylindrical sporangia containing a longitudinal pair of motile spores forming singly or in bundles on short ramifications of the aerial mycelium, was isolated from soil collected from an evergreen forest in Thailand. The cell-wall peptidoglycan contained meso-diaminopimelic acid. The whole-cell sugars contained ribose, madurose, mannose and glucose. The predominant menaquinones were MK-9(H2). Mycolic acids were not detected. The diagnostic phospholipids were phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylinositol, phosphatidylglycerol, phosphatidylinositol mannoside, diphosphatidylglycerol and aminophosphoglycolipid. The predominant cellular fatty acids were unsaturated C17 : 1, C18 : 1, saturated C16 : 0, and C17 : 0. The G+C content of the DNA was 70.8 mol%. Phenotypic and chemotaxonomic analyses showed that the isolate had the typical characteristics of members of the genus Planobispora. Furthermore, 16S rRNA gene sequence analysis also indicated that this strain belonged to the genus Planobispora but as a putative novel species. DNA-DNA relatedness values that differentiate the isolate from previously described members of the genus Planobispora were significantly below 70 %. Following an evaluation of phenotypic, chemotaxonomic and genotypic studies, it is proposed that the isolate represents a novel species, Planobispora siamensis sp. nov.; the type strain is A-T 4600(T) ( = BCC 39469(T) = NBRC 107568(T)).