Suckling behavior of primiparae in free-ranging Japanese macaques (Macaca fuscata) was compared with that of multiparae at Jigokudani Monkey Park, the Shiga Heights, Nagano Prefecture, Japan, from April 1984 to 1994. The estimated rates of milk secretion in a single preferred nipple among primiparae were lower than those among multiparae from birth to 5 months of age. Milk secretion capabilities of primiparous mothers, hence, appear to be inferior to those of multiparous mothers. In nutritive suckling, although Japanese macaque infants preferred one single nipple, nipple preferences in primiparae were weaker than those in multiparae. With supplementary two-nipple use during suckling, however, the infants of primiparae appear to overcome a suckling flaw of their primiparous mothers. After infants were 5 months of age and after a drop (from approximately 10% to approximately 5%) in the rates of milk secretion, however, milk secretion rates in a single preferred nipple among primiparae were similar to those in multiparae and the supplementary two-nipple use in primiparous mother-infant dyads disappeared.