Abstract: The leaf extracts of 5 cultivars of Citrus sinensis Osb. and 50 biotypes of mandarin were analyzed by polyacrylamide gel electrophoresis for isozymes of peroxidase glutamate oxaloacetate transaminase, tetrazolium oxidase, phosphoglucose mutase, phosphoglucose isomerase, superoxide dismutase, malic enzyme and esterase. Dissimilarities of the isozyme patterns among the samples were calculated by computer based on the UPGMA method to demonstrate the affinity relationships of the samples. The mandarins arose from polyprototypes. The small-fruited mandarins were the primitive forms. It seemed better to consider ‘Daoxian wild mandarin', ‘Mapiju mandarin'or‘Goushikan mandarin' as the type species of mandarins originated in China, "Kan" (large-fruited mandarins, eg, satsuma mandarin) might originate in two ways. One was hybridization between "Chu" (small-fruited mandarins such as ponkan) and C. sinensis, the other was just the variation of "Chu". C. tankan Tan. was a hybrid of 'Ponkan mandarin' (C. reticulata Blanco )and C. sinensis, C. unshiu Marc, might originate from the nucellar mutation of C. nobilis Lour, cv. Huangyanben diguangju.