The purpose of the present study was to investigate age differences in narcissistic tendency during adolescence. Narcissistic tendency of 489 participants, junior and senior high school students and college undergraduates, was measured with Narcissistic Personality Inventory, Short Version (NPI-S). Results showed an increase in the tendency along with the age, but no significant difference was found between boys and girls. However, detailed examination revealed different patterns of developmental changes over time in subscales of NPI-S, and therefore further examination of age differences in them appeared to be necessary.