Abstract: The name Hydrocotyle was first proposed by Tournefort (1700) on the basis of the european species H. vulgaris and the genus was later accepted by Linnaeus (1753). The hitherto known classical work of the genus was a monograph by A. Richards (1820). Since the time of Bentham (1861), Maximowicz (1886), Forbes and Hemsley (1887), Diels (1900), Boissieu (1906), Hayata (1908, 1912), Dunn and Tutcher (1912), Wolff (1929), Masamune (1932) and Handel-Mazzetti (1933) etc., a dozen of chinese species has been described from various collections from China. Nevertheless, it is not surprising to note that the chinese species of the genus are incessantly increasing, and thus a systematic treatment is in need. The genus has about 75 species chiefly of tropical and subtropical regions; more than forty species are found in South America, the rest of the species occurs in North America, Africa and southeastern Asia. In various parts of Asia, four are being reported from Japan, three from Indonesia and Burma, two from Viet-Nam and Malaya, seven from India, but only one species occurs in Korea, Philippines, Bhutan, Sikkim and Nepal. Sixteen species are found in the warm part of China extending from Lat. 20°-34°N. and Long. 98°--123°E., i.e. east from Kiangsu and southwestward to Szechuan and Yunnan with their center in the southwestern provinces. Among them H. nepalensis Hook. and H. sibthorpioides Lam. are two widely distributed members ranging over 11 provinces east from Chekiang, Anhwei and westward to Szechuan and Yunnan; H. wilfordi recorded from 7 provinces including the eastern coastal and the southwestern provinces. H. pseudo-conferta Masam. is recorded from Chekiang, Taiwan and probably Yunnan; H. javanica var. chinensis Dunn from Hunan, Szechuan and Yunnan, H. wilsonii from Hupeh and Szechuan, and H. ramiflora from Chekiang and Taiwan. The indian species H. hookeri and the newly described species H. salwinica are known in Yunnan. Ecologically, they are plants of warm, moist or wet sites, such as under the shade of forest, along the streams, river banks and water ditches. The present paper accounts for 13 species and 1 variety with their diagnostic characters and geographical distributions noted. H. salwinica from Salwin valley of Yunnan, collected by prof. T. T. Yu, has been described as a new entity, and the binominals of H. wilsonii Diels and H. javanica var. chinensis Dunn, which appear only in names on herbarium specimens, are validated with latin descriptions. Analytical key for the listed species is provided. In addition to the above mentioned species, H.forrestii Wolff from Yunnan, H. formosana Hayata and H. setulosa Hayata from Taiwan are also listed here, although no specimens have been represented in our collection. The original diag-noses of the corresponding species are thus included for further elucidation.