Among the marine toxins related to human intoxication, tetrodotoxin has been known as one of the most prejudicial. Two tetrodotoxins, namely PFT-1 and PFT-2 were isolated and purified from liver of puffer fish by thin layer chromatography. The structure of both the toxins was elucidated by means of IR, 1H-NMR and 13C-NMR and mass spectroscopy. Sub acute toxicity study showed that both the toxins had pronounced effects on total RBC, WBC, platelet and ESR. Further serum levels of SGPT, SGOT, SALP, bilirubin, creatinine and urea are also affected by the toxins. The histopathological examinations showed that all the tissues such as liver, lung, heart and kidney of rat were severely changed after treatment with the toxins. The toxicity of the purified compounds, PFT-1 and PFT-2 were also performed by brine shrimp lethality bioassay.