In this study we developed the analytical methods for the determination of three neurotoxin; anatoxin-a, saxitoxin and neosaxitoxin using HPLC/FLD system and this analytical methods were applied to real sample; algae culture and algae extracts. For the HPLC/FLD analysis of anatoxin-a samples were concentrated on WCX(Weak Cation Exchanger) SPE and then anatoxin-a in concentrate was derivatized with NBD-F solution. Supernatant was injected on HPLC system. For the HPLC/FLD analysis of saxitoxin and neosaxitoxin samples were separated on the column and then derivatizied by post column reactor for fluorescen detection. For post column reaction of saxitoxin we feed two kinds of reaction solution; Oxidizing Reagent of which composition was periodic acid(7mM) in 50mM potassium phosphate buffer, pH 9 and acidifying reagent of which Composition was 0.5M acetic acid. The LOD value for anatoxin-a, saxitoxin and neosaxitoxin in HPLC/FLD method was 24.3 ng. $35{mu}g/L$, $27{mu}g/L$ respectively. We determined the anatoxin-a content of lyophilized anabaena flos-aquae and $20{mu}g/g$ d.w. of anatoxin-a was detected. We analyzed saxitoxin and neosaxitoxin in algae culture media and extracts of lypopyllized algal cell cultured and that of Deachung reservior. Saxitoxin and neosaxitoxin in real sample were below the limit of detection. Although there are various water treatment processes for removing neurotoxins were suggested no process give simultaneous and complete removal of neurotoxins. It was cocluded that nanofiltration which reject material by size can be a process for removal of neurotoxins.