Progesterone levels were measured by radioimmunoassay in the last milk of seven dairy cows in 5-75 days post-partum. The progesterone levels were from 0.1 to 1.5 ng/ml and averaged 0.4 +- 0.2 ng/ml for the last milk of the seven cows. A range of 0.3 to 0.7 ng/ml for average progesterone levels of the seven cows can be estimated. Two ovarian cycle activities in post-partum of cow No. 43 were observed and a ovulation on 15-20 days post-partum was revealed. The peak value after 20 days post-partum was 3.0 ng/ml. The progesterone level after peak value was declined, and reached to about 0.2 ng/ml on 35 days post-partum. The changes of ovarian activities were exhibited again in 35-55 days post-partum. The progesterone levels of cow No. 43 were lower in luteal phase oestrous cycles post-partum than that from the other cows in normal luteal phase oestrous cycles.