An actinomycete, designated strain GIMV4.0001(T), was isolated from a forest soil sample in Vietnam. It produced white aerial mycelium and violet-blue diffusible pigment on Gause's synthetic agar. The substrate mycelium colour was not sensitive to pH. Micoscopic observations revealed that strain GIMV4.0001(T) produced long, straight chains of cylindrical spores, and chemotaxonomic data confirmed that it belongs to the genus Streptomyces. Melanin was produced, but no antibacterial activity was evident against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans or Penicillium citrinum. Analysis of the 16S rRNA gene sequence of strain GIMV4.0001(T) revealed that the highest similarity (99.4 %) was to Streptomyces bikiniensis ATCC 11062(T). However, the DNA-DNA relatedness between strain GIMV4.0001(T) and S. bikiniensis ATCC 11062(T) was found to be 50.3 %. Strain GIMV4.0001(T) could also be differentiated from S. bikiniensis ATCC 11062(T) and other Streptomyces species showing high 16S rRNA gene sequence similarity (98-99 %) based on morphological, physiological and biochemical characteristics. On the basis of its physiological and molecular properties, it is evident that strain GIMV4.0001(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces vietnamensis sp. nov. is proposed. The type strain is GIMV4.0001(T) (=CCTCC M 205143(T)=IAM 15340(T)).