Nine species of benthic dinoflagellates isolated at Ishigaki Island, Okinawa, were grown unialgally. They were Prorocentrum lima, prorocentrum concavum, prorocentrum rhathymum, Amphidinium carteri, Amphidinium klebsii, Coolia monotis, Ostreopsis siamensis, Ostreposis ovata, and Gambierdiscus toxicus. The harvested cells were extracted with boiling methanol and the extracts were fractionated into diethyl ether soluble, 1-butanol soluble, and water soluble fractions. Each fraction was tested by mouse and fish assays and by blood cell hemolysis test. The extracts of P. lima, P. concavum, A. carteri, A. klebsii, O. siamensis, O. ovata, and G. toxicus were confirmed to show toxicity to mice. Hemolytic activity was recognized in all the species tested. Ichthyotoxicity was demonstrated by A. carteri, A. klebsii, and P. concavum, the last being the most potent. With the exception of the water soluble toxin of O. siamensis, all the toxins were found in either diethyl either diethyl ether soluble fraction or 1-butanol soluble fraction or in both.