The characteristics of corpora lutea during the early(Day 1-5), mid(Day 6-10), late(Day 11-15) and regressed stages(Day 16-20) of the estrous cycle were studied from the ovaries of slaughted Korean native cows. The concentrations of serum progesterone in normally cycling Korean native cow were determined by radioimmunoassay (RIA) and the concentration of cholesterol was assayed by assay kit. There were no significant differences in the weight of ovaries and corpora lutea throughout the estrous cycle. However, the ratio of corpora lutea weight to ovarian weight were higher(about 44%) in mid and late corpora lutea than in early and regressed corpora lutea, but that was not significantly different. The concentrations of cholesterol and protein in cytosol of regressed corpora lutea wire significantly lower than in those of functional corpora lutea(P$lt;0.05). The concentration of semen cholesterol way higher on Day 13 than un Day 8 in cycling Korean native Cows. and maintained about 140㎎/㎗ from Day 12 to Day 20. The concentration of serum progesterone was higher on Day 0 (2.45ng/㎖) than on Day 3(1.87ng/㎖), and then maintained about 7 ng/㎖ to Dau 17 and afterwards decreased drastically towards on Day 20(2.6ng/㎖). Thus, progesterone secretion on Day 0 of the estrous cycle may be secreted in luteal cell of regressed corpus luteum or in preovulatory Graffian follicle.