This study was conducted to find out the changes of progesterone and estrone sulphate concentration in serum of Korean native goats throughout gestation, and to apply the serum levels of the hormones to pregnancy diagnosis. Serum concentration of progesterone and estrone sulphate were assayed by radioimmunoassay. Serum progesterone concentration was similar to its luteal phase values during early pregnancy and remained at the high level continually at 20∼140days and decreased rapidly at the day of parturition. Serum estrone sulphate concentration showed to increase markedly at 40∼50dyas gestation and steadily increased to the maximum of 7.13ng/ml at 140days, but declined sharply at the day of parturition. The accuracy of pregnancy diagnosis by the measurement of serum progesterone at 20∼24days after mating was 85.7∼92.3% and that of non-pregnancy diagnosis was 100%, when the serum progesterone levels higher and lower than 3.0ng/ml were supposed to indicate pregnancy and non-pregnancy, respectively. The accuracy of pregnancy diagnosis by the mearsurement of serum estrone sulphate was found to be nearly 100% since 50days after mating, when the serum levels of estrone sulphate higher then 0.5ng/ml were diagnosed to be pregnant. The optimal sampling time for pregnancy diagnosis was considered to be at 50 days after mating or to be later. It appears that estrone sulphate values above 7.0ng/ml at any time in gestation are highly indicative of twin. But there was found no significant difference(P<0.05) in serum estrone sulphate concentration and number of kids between does with single and twin kids.