A variety of animals often rely on learning for adjusting foraging behavior. Many species of the ants feed on nectar secreted from various insects and plants and have mutualistic association with them by patrolling on the nectar reward. To explore the effect of the ant learning on the mutualistic association, we conducted laboratory behavioral assays using the ants, Pristomyrmex punctatus and the lycaenid butterfly, Narathura japonica. The results showed that (1) the ants can learn to recognize lycaenid caterpillars as partners and enhanced tending behavior by associating caterpillar's odor with the nectar rewards, (2) Enhanced tending behavior was maintained at least 7 days, so that the caterpillar’s information was stored in long-term memory, (3) When the naïve workers were reared with the learned workers, the naïve workers also enhanced tending behavior toward the caterpillars. These results suggested that caterpillar’s odor was used as an important cue to learn, memorize and identify rewarding partner species, and the learned chemosensory preferences spread through ant colonies via social interaction.