A Gram-positive aerobic actinomycete, designated SR14.14 T, isolated from the rhizospheric soil of rubber tree was determined taxonomically using a polyphasic approach. The organism contained meso-diaminopimelic acid and the N-acetyl type of peptidoglycan. The predominant menaquinones were MK-9, MK-9(H 2) and MK-9(H 4). Madurose was detected in the whole-cell hydrolysates. Mycolic acids were not presented. Major phospholipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol mannoside. Major cellular fatty acid was iso-C 16: 0 and the GC content was 71.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequence suggested that the isolate belongs to the genus Sphaerisporangium. The sequence similarity value between the strain SR14.14 T and its closely related species, Sphaerisporangium album, was 97.8%. DNA-DNA hybridization values between them were well below 70%. Based on genotypic and phenotypic data, strain SR14.14 T represents a novel species in the genus Sphaerisporangium, for which the name Sphaerisporangium siamense sp. nov. is proposed. The type strain is SR14.14 T (BCC 41491 T NRRL B-24805 T NBRC 107570 T). © 2011 Japan Antibiotics Research Association. All rights reserved.