The purpose of the study was to investigate the effects of detraining on the serum lipids level in athletes. 10 male athletes(rowing and swimiming) and 5 female athletes(rowing) were studies during 3 week detrainig periods. Venous blood samples were drawn from ante cubital vein using syringes(7ml/each) at 4 times(0, 1, 2, 3 wk). The blood samples were used to analyze the level of blood TC, HDL-C and TG. TC and TG were analyzed by enzyme method and HDL-C was analyzed by dextran sulphate MgCl₂ precipitation method. After Chemical treatemt, exact values were obtained by spectro photometer 2600(Gilford, U.S. A.), and TC/HDL-C ration and LDL-C ［TC-(TG /5+HDL-C) : Assmann, 1982］ were calculated afterwards. The conclusions were summarized as follows : · Changes of blood lipids level were revealed from 1 week after detraining and made a more increased(or decreased) from 2 week after detraining. · Changes of blood lipids level during 3 week detraining periods were showed higher difference between sexes than that of sport events. · Changes of blood lipids level during detraining periods were showed higher sensitivity at male than that of female. athletes.