During the period from December 1986 to Agust 1987, 224 women who attended the post partum clinic, at Srinagarind Hospital were-studies. Their ages ranged from 15-40 years old with the majority between 21-25 years, Most of them were primipara, farmers and had less than primary school education Endometrial samplings were taken at the first post partum visit. Most of them were lactating and had adequate mount of breast milk. However 19.64 percents of them already had menstruation and 30.80 percents had sexual intercourse before post partum check up. Sexual intercourse mostly began at 1 month post parturition. Endometrial biopsy revealed ovulation in only 1 case which was at 43 days after delivery.