A strain of Raphidiopsis (Cyanobacteria) isolated from a fish pond in Wuhan, P. R. China was examined for its taxonomy and production of the alkaloidal hepatotoxins cylindrospermopsin (CYN) and deoxy-cylindrospermopsin (deoxy-CYN). Strain HB1 was identified as R. curvata Fritsch et Rich based on morphological examination of the laboratory culture. HB1 produced mainly deoxy-CYN at a concentration of 1.3 mg·g−1 (dry wt cells) by HPLC and HPLC-MS/MS. CYN was also detected in trace amounts (0.56 μg·g−1). A mouse bioassay did not show lethal toxicity when tested at doses up to 1500 mg dry weight cells·kg−1 body weight within 96 h, demonstrating that production of primarily deoxy-CYN does not lead to significant mouse toxicity by strain HB1. The presence of deoxy-CYN and CYN in R. curvata suggests that Raphidiopsis belongs to the Nostocaceae, but this requires confirmation by molecular systematic studies. Production of these cyanotoxins by Raphidiopsis adds another genus, in addition to Cylindrospermopsis, Aphanizomenon, and Umezakia, now known to produce this group of hepatotoxic cyanotoxins. This is also the first report from China of a CYN and deoxy-CYN producing cyanobacterium.