We increase the known reptile and amphibian fauna of Nan Ao Island, in the South China Sea, Guangdong Province, from 19 species in 1999 to 45 currently. Among these additional 26 species, six were published by 2004, six in 2011, and 14 are first reports for Nan Ao: Trachemys scripta, Takydromus sexlineatus, Scincella modesta, Amphiesma stolata, Boiga multomaculata, Myrrophis chinensis, Myrrophis plumbea, Ptyas korros, Ptyas mucosus, Bungarus multicinctus, Naja atra, Hoplobatrachus rugulosus, Hylarana taipehensis, and Paa spinosa. The herpetological fauna of Nan Ao has three geographic patterns. We add two more species of austro-boreal disjunction to the previous known six examples: Scincella modesta and Oligodon formosanus. Additionally, Scincella modesta, Coelognathus radiatus and Oocatochus rufodorsatus each has a trans-Beringian closest North American counterpart, rendering five species with Grayian distribution on Nan Ao. Furthermore, among 21 species with imbalanced distribution between the eastern and western massifs within Nan Ao Island, 16 are only on the eastern massif and 5 only on the western. The implications of this within-island heterogeneity and the other two biogeographic patterns are discussed.