Alliance formations in a troop of free-ranging Japanese macaques, which had been provisioned 16 months before the present study was begun, were observed at the feeding ground for about 300 hr from April 1973 to March 1974. The patterns of alliance formations and their roles were described. The leader male had a quite unique role in his alliance formations; he allied much frequently with the aggressees and attacked the aggressors. Besides, the leader male allied more frequently with babies, yearlings, 2-year-old animals, and adult females, while he frequently attacked the 3- and 4-year-old animals and adult males. The animals who belonged to the same matrilineal group always allied with one another. Except the leader male, the troop members rather preferred to ally, except in those cases where the former diads involved their matrilineal group members, with the first aggressors. Networks of such alliance formations in relation with the social organization of Japanese macaques are discussed.