[Objectives] The genus Atlanta Lesueur, 1817 (Mollusca:Gastropoda:Littorinimorpha:Atlantidae) comprises small, holoplanktonic gastropods that are an important component of marine zooplankton communities. While 21 species are recognized globally, only eight have been documented from the China Seas. This study aims to investigate the species diversity of the genus Atlanta in the South China Sea through detailed morphological analysis, with the objective of identifying and describing potential new records for the China Seas, thereby updating the regional biodiversity inventory. [Methods] Zooplankton samples were collected during four research cruises covering the northern, northeastern, western, and southern regions of the South China Sea between 2022 and 2023. A total of 63 samples were obtained via plankton nets with mesh sizes ranging from 160 to 500 μm and were preserved in a 5% formaldehyde solution neutralized with sodium borate to prevent shell dissolution. In the laboratory, a Nikon SMZ18 stereomicroscope was used to sort and identify the specimens. For detailed morphological examination, shells and opercula were cleaned via ultrasonication, dehydrated, dried, and sputter-coated with gold. High-resolution imaging was performed via a Hitachi S-3400N scanning electron microscope (SEM) to observe critical diagnostic features such as fine shell sculpture, protoconch morphology, and opercular structures. Morphometric measurements, including maximum shell diameter and whorl count, were recorded for representative specimens. [Results] A total of 12 Atlanta species were identified in the South China Sea (Table 2; Fig. 2). Among them, four species—A. echinogyra Richter, 1972; A. plana Richter, 1972; A. frontieri Richter, 1993;and A. oligogyra Tesch, 1906—were reported as new records for the China Seas. Detailed morphological descriptions and measurements for these four species are provided (Tables 3 ~ 6; Figs. 3 ~ 6). Key diagnostic features and size ranges are as follows:1) A. echinogyra (max shell diameter:1.507 mm) is distinguished by its reddish-purple spire with complex sculpture and a spiny opercular gyre (Fig. 3, Table 3). 2) A. plana (max shell diameter:3.230 mm) is characterized by a very flat shell and a low spire with subtle spiral ridges (Fig. 4, Table 4). 3) A. frontieri is identified by a distinctive spiral rib running along the suture from the second to the fourth whorl (Fig. 5, Table 5).4) A. oligogyra (max shell diameter:2.323 mm) features a globular spire with shallow sutures (Fig. 6, Table 6). The spatial distribution of these species within the South China Sea is mapped in Fig. 7. It revealed that A. plana and A. oligogyra were relatively common and widespread; A. echinogyra was mainly found in the southern and western regions; A. frontieri was rare and restricted to the western region. [Conclusion] The discovery of these four new records increases the known diversity of the genus Atlanta in the China Seas from eight to twelve species. All species are typical warm-water taxa, and their presence aligns with the tropical nature of the South China Sea. This study provides crucial morphological and distributional data that not only enrich the marine zooplankton biodiversity inventory of China but also establish a foundational basis for future ecological and biogeographical research on this ecologically significant group. All voucher specimens are deposited in the Marine Biodiversity Collection of the South China Sea, Chinese Academy of Sciences.