The authors investigated the behavioral aging effects of Japanese macaques in 3 object discrimination learning tasks: learning-set (LS) formation, go/no-go discrimination learning, and multiple discrimination reversals. Aged monkeys showed deteriorated performance in these tasks compared with younger controls, Hypothesis analysis of LS showed that aged monkeys had difficulty learning the lose-shift component of the hypothesis win-stay-lose-shift with respect to object. Deficits in go/no-go successive discrimination were clear in no-go trials only in the first 2 pairs of 5 tasks. Performance of aged monkeys was severely disturbed from a chance to criterion level in discrimination reversals. These results are attributed not only to increased tendency for perseveration but also to difficulty in associating the reward and the object in aged monkeys and may be related to the decline in the functions of the ventral frontal cortex.