Kurahyne B (2), a new analogue of kurahyne (1), was isolated from the marine cyanobacterium Okeania sp. Its gross structure was elucidated based on spectroscopic analyses, and the absolute configuration was established by total synthesis. Kurahyne B (2) inhibited the growth of both HeLa and HL60 cells, with IC50 values of 8.1 and 9.0 μM, respectively. The growth-inhibitory activity of kurahyne B was the same as kurahyne (1). In parallel, the first total synthesis of kurahyne (1) was also achieved.