During a screening for novel and biotechnologically useful actinobacteria in insects, a novel actinobacteria with antifungal activity, designated strain 5H-CA11(T), was isolated from the head of an ant (Lasius flavus) and characterized using a polyphasic approach. The organism was found to have morphological and chemotaxonomic characteristics typical of members of the genus Streptomyces. 16S rRNA gene sequence analysis showed that strain 5H-CA11(T) is a member of the genus Streptomyces, with the highest sequence similarity to Streptomyces scabrisporus DSM 41855(T) (98.9%). Similarities to other type strains of the genus Streptomyces were lower than 96%. Phylogenetic analysis based on the 16S rRNA gene sequence also indicated that strain 5H-CA11(T) clusters with S. scabrisporus DSM 41855(T) using two tree-making algorithms. DNA-DNA hybridization between strain 5H-CA11(T) and S. scabrisporus JCM 11712(T) revealed 33.6% similarity, supporting the phenotypic and phylogenetic differences found between these two strains. Therefore, the strain is concluded to represent a novel species of the genus Streptomyces, for which the name Streptomyces lasii sp. nov. is proposed. The type strain is 5H-CA11(T) (=CGMCC 4.7303(T) = DSM 102043(T)).