Cyprinus pellegrini Tchang is an important food in both Singyun Lake and Chiloo Lake,attaining some 70% and 30% of the total yields of these lakes respectively.In this paper,the results of the biological study and the situa- tion of intraspecific differentiation of this fish in these lakes are presented. Age determination has been made on scales,the annuli being demarcated by intersection of the adjacent bands of circuli.Actual measurements of the body lengths and weights for various ages and the calculated boty lengths from scale reading are given.The fish measure on average 135 mm in body-length when one year old,197 mm,242 mm,and 288 mm when 2-year old to 4-year old of age respectively. The length-weight relationship of Cyprinus pellegrini of Singyun Lake can be expressed by the equation W=0.00001283L^(3.0917),and that of Chiloo Lake, by W=0.00002181L^(2.9875).Graphic representation of these two equations indi- cates that with the lengths being the same,the fish of Chiloo Lake possesses a greater body weight. This fish partly attain maturity when 1-year old and all are mature at 2- years of age.The breeding season of this fish in both lakes extends from April to September,but most individuals lay eggs in May and June.The eggs are adhesive,and are usually deposited on higher aquatic plants. Food studies based on contents of digestive tracts show that this fish is a zooplankton feeder.It feeds chiefly on cladocerans and copepods. Analysis of body-length composition of five catches,comprising nearly 2000 individuals,points to the preponderance of 1-year old and 2-year old age groups, individuals of more advanced age being rare in the catches.This leads us to think that the stock is on the way of diminishing as an effect of intentive fishing. Suggestion with regard to fishery management in these lakes is proposed.