A severe poisoning case with typical paralysis symptoms was reported in Tinh Gia District, Thanh Hoa Province, Vietnam on 27 March 2021 by consumption of some marine crabs. Two specimens as remaining suspected poisonous food were collected for toxin analysis. Based on recorded poisoning symptoms, tetrodotoxins and saxitoxins in crab specimens which identified as belonging to Demania reynaudii were examined in HILIC/MS-MS. As result, TTX (14.02 and 14.80 g/g), 4epi-TTX (3.40 and 7.12 g/g) and Anh-TTX (40.00 and 55.75 g/g) was detected in the extracts from two specimens. Toxicity in the specimens (174.6 and 194.5 MU/g) were much higher than consumption level for TTXs (10 MU/g) suggested in Japan. A consumption of 2 big specimens (137 g b.w.) or 5 small ones (71.2 g b.w.) containing these toxicity was enough to cause poisoning even fatal for human. It is indicated that xanthid crab D. reynaudii is not safe for food. The present study confirmed TTX was toxin implicated to poisoning by consumption of D. reynaudii in Tinh Gia District, Thanh Hoa Province on 27 March 2021, and it was the first report about this TTX bearing-crab species in Vietnam.