With the expansion of e-commerce, an increasing number of Chinese consumers are turning to online markets to purchase foreign seafood. When buying seafood online, customers cannot physically evaluate the product, and the market Web page instead of the seafood label conveys all of the product information. However, specific regulations concerning the information presented on the Web page have not been created, which may foster seafood fraud and misdescription. Because mislabeling of seafood has become a widely reported issue in the Chinese offline market, the online scenario must be investigated comprehensively. This study focused on various seafood products that originated from 20 countries and were sold by one of the largest e-commerce companies in China. For each country, only the product with the greatest overall monthly transaction volume was selected, and 5 samples were purchased per product for a total of 100 samples. The Web page description (including the heading of the Web page and the description of the commodity) and the label of the received products were compared to evaluate the description consistency. DNA barcoding technology was used for seafood species identification, and the scientific names retrieved from the sequence analysis after consulting the Barcode of Life Data systems and GenBank were compared with the expected species, genus, and family to determine the description authenticity. Only 25% of the samples had consistent descriptions on the Web page and on the label of the received product. Most of the inconsistency originated from the geographical origin, and only four products (G10, G50, G19, and G69) had inconsistent species, genus, and family descriptions. Molecular analysis revealed that in 65% of samples the species was correctly described. The online seafood market presents challenges regarding seafood fraud and opportunities for seafood species substitution.