Advantages of breast feeding can be traced to a number of its unique properties which includes its nutritional and extra nutritional contributions associated with longer birth spacing. Twenty-five lactating and 10 non lactating (control) women were studied to see the effect of breast feeding on ovulation keeping in consideration all the important factors which effect resumption of ovulation during lactation like age, parity, body weight, education, frequency of breast feeding and supplementary feeding to the infant. Serum progesterone was studied for non lactating women while for lactating women milk progesterone was also studied. A low serum progesterone was found in lactating women as compared to non lactating. A low milk progesterone was also observed in lactating an-ovulatory as compared to ovulatory. The frequency of suckling, breast feeding on demand and gradual introduction of supplementary feeding were found to be the most important factors.