Detection of tetrodotoxin（TTX）in aquatic products is a hot topic of research in food security field. Although the mouse bioassay is the current standard method with high sensitivity, its quality and quantification are poor. Detecting TTX by high performance liquid chromatography (HPLC) can improve quality and quantification. In China, the detector of the popular HPLC method is UV detector, its sensitivity and quality can’t satisfy the food security standard. This article is researching determination of TTX in aquatic products by post column derivation HPLC. The separation characteristic of HPLC and fluorescence detector with selectivity and high sensitivity effectively improve sensitivity, quality and quantification, which make this method satisfy the food security standard. Takifugu and Nassarius were selected as the main research objects. Sample was extracted with 0.1% acetic acid, and then purified with C18 solidphase extraction cartridge. TTX was separa ted by reverse phase ionpair liquid chromatography, of which ionpair reagent was heptanesulfonic acid sodium salt, then heated with 4 mol·L^-1 NaOH at 110 ℃ in online derivation system. It was converted to C9base with fluorescence characteristic, quantified by fluorescence detector. Good linearity was observed: the linear range was 5-1 600 ng and linear relationship r=0.9997. For the 1, 2, 8 μg·g^-1 spiked samples, withinday and daytoday recoveries were 80.9%-91.2%, RSDs were 1.93%-5.57%, and the limitation of quantification were 1 μg·g^-1. This method was good quality because of no interference peak near the TTX target peak in the chromatogram of spiked sample. When a poisonous Takifugu was detected by post column derivatization HPLC and mouse bioassay simultaneously, the results of the two methods were consistent. From the results of above, detection of TTX in aquatic products by post column derivation HPLC is feasible.