In beef cows, a milk yield showed an inhibitory effect on both the postpartum ovarian activity and the uterine involution. The suckling stimulation, however, indicated a suppressive effect on the former, while a hastening effect on the latter. This conclusion was derived from the results of multiple regression analyses on suckling cows, which were subjected to restricted sucklings twice a day and early weaning. In estimating adequate intervals from calving to first ovulation, following were the relevant factors in order of decreasing importance: parity > milk yield > body weight changes caused by nutrient conditions > suckling stimulation. The factors affecting uterine involution could also be ranked as follows in decreasing order of importance: parity > milk yield > sucking stimulation. The uterine involution was more stable than the postpartum ovarian activity in terms of the sensitivity to some critical factors