The purpose of this work is to summarize our present knowledge of the Acereous plants of Chinai, Since Pax published his last monograph of Aceraceae2 in 1902, the multiplicity of new species and the huge collections of material which are not easily identified, have particularly emphasized the somewhat pressing requirement for a critical review and the necessity for supplementary descriptions and special notes. This work was continued over a period of more than five years. During this time various herbaria were visited where type- specimens and numerous collections were carefully examined. The main work has been done at the Royal Botanic Garden, Edinburgh. I am greatly indebted to Professor Sir William Wright Smith, who has given me continual encouragement during the course of my work. My best thanks are also due to Dr. J. M. Cowan for invaluable suggestions and criticism; to Mr. W. E. Evans for special arrangement of material; to Cdr. J. T. Johnstone for assistance in gathering literature, and to Dr, H. R. Fletcher for his critical reading of some parts of the manuscript. I should like also to tender my sincere thanks to Professor S. S. Chien of the Biological Laboratory of the Science Society of China, Nanking, under whose supervision I laid the basis of my work there. I am very obliged to Professor A. Rehder of the Arnold Arboretum, Jamaica Plain, Massachussetts, U.S.A.; Professor H. Handel -Mazzetti of the Botanic Institute and Garden, Vienna, Austria; Professor H. H. Hu of the Fan Memorial Institute of Biology, Peiping; Professor W. Y. Chun of the Botanic Institute of Sun - Yatsen University, Canton; and to Professor F. P. Metcalf of the Lingnan University, Canton, for their kindness in sending me material, and valuable suggestions on some special problems. My warmest thanks are also due to the authorities of various herbaria - too numerous to be mentioned individually - who sent specimens on loan. I wish to express my special acknowledgment to Mr. J. Ramsbottom of the Department of Botany, British Museum (Natural History, London; to Sir Arthur W. Hill and Dr. A. D. Cotton of the Royal Botanic Gardens, Kew, England; to Professor L. Diels and Professor R. Pilger of the Botanic Museum, Berlin -Dahlem, Germany; to Professor F. Pax and Professor H. Winkler of the Botanic Institute, Breslau, Germany; to Professor K. Sussenguth of the Botanic Garden, Munich, Germany; to Dr. K. Keissler of the Natural History Museum, Vienna, Austria; to Professor F. Knoll of the Botanic Institute and Garden, Vienna, Austria; to Professor G. Negri and Professor A. Messeri of the Botanic Museum, Florence, Italy; and to Professor H. Humbert of the Natural History Museum, Paris, France, for their courtesy in granting me the privilege of examining specimens in their herbaria