Abstract: Tetrodotoxin (TTX) is a potent marine toxin, found in a great variety of marine and some terrestrial species. Inorder to explore the potential bacterial sources of TTX in Nassarius semiplicatus, we collected its TTX and analogues from Fujian Province and analyzed them by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Besides, we compared the microbial communities of TTX-bearing and non-TTX-bearing by using high-throughput sequencing technology. The results show that the contents of TTX in TTX-bearing N. semiplicatus (LTN) were 402~644 μg·kg⁻¹. TrideoxyTTX, dideoxyTTX and deoxyTTX were detected. TTX and other analogues were not detected in non-TTX-bearing N. semiplicatus (NTN) except dideoxyTTX. The results of high-throughput sequencing show that the community richness of LTN was significantly higher than that of NTN (p<0.05). The microbial communities of LTN and NTN were dominated by Proteobacteria. TTX-producing bacteria, including Vibrio, Pseudoalteromonas and Psychrobacter, were the dominant bacteria in LTN, while Pseudoalteromonas and Shewanella in NTN. The significant difference analysis shows that the relative abundance of 17 differential genera in LTN,including Vibrio and Psychrobacter, etc., were significantly higher than that of NTN (p<0.05). The KEGG functional composition of the intestinal flora of LTN and NTN were similar. The main metabolic pathways were amino acid metabolism, carbohydrate metabolism and so on. The results show that TTX-producing bacteria can exist in both LTN and NTN; Vibrio and Psychrobacter are more enriched in LTN. These TTX-producing bacteria may be related to the biosynthesis of TTX analogues andprecursors in N. semiplicatus.