The Paralytic shellfish neurotoxins (PST) are of increasing interest for biomedical applications. The chemical synthesis is often complex and expensive that’s why the purification by membrane filtration of PST from Alexandrium minutum dinoflagellate was investigated. Disrupted micro-alga cells by ultrasonic treatment were diafiltred to let pass toxins through an ultrafiltration membrane. Then, the mean permeate was concentrated and diafiltrated by nanofiltration. Mean permeate fluxes equal to 187, 135 and 135 L h−1 m−2 were obtained during the first diafiltration, the concentration step and the final diafiltration respectively. Up to 57% (mol/mol) and 78% (mol/mol) of organic matters and salts were removed respectively. Divalent ions were sparsely removed contrary to monovalent ones. C1 and C2 toxins were successfully purified since more than 75% (mol/mol) were recovered. However, only 27 to 50% (mol/mol) of GTX2, GTX3 and STX were recovered.