Dolichospermum is a filamentous cyanobacterial genus with the potential capacity to produce multi-cyanotoxins and taste and odour (T/O) compounds. Twenty-four strains of Dolichospermum isolated from Lake Zhelin, Jiangxi were morphologically and molecularly characterized for exploring the biological properties of Dolichospermum species. They were classified into four species as D. planctonicum, D. affine, D. circinale and D. spiroides. Phylogenetic analysis based on the 16S rRNA sequences showed that all Dolichospermum strains here were highly similar to the strains isolated from Japan and other regions, but only D. affine was well grouped into one cluster. Based on the secondary structures of 16S-23S ITS, all the Dolichospermum strains showed to have the same structures in D1-D1' region. In Box-B and V3 regions, the structures of D. planctonicum and D. affine were different from those of D. circinale and D. spiroides, indicating the significant difference between two morphological types (coiled and straight type). Based on the DNA molecular detection, the 24 strains of Dolichospermum were not cyanotoxin producers, but four strains of D. planctonicum and one strain of D. circinale showed to contain geosmin synthase gene. Such results not only presented the basic scientific information on biodiversity of bloom forming cyanobacteria and their ecological risk in Lake Zhelin, but also provided the basis on aquatic ecosystematic studies and protection along Lake Poyang watershed.