This study investigates the influences of narcissism and emotional self-disclosure on depression and happiness levels of high school students. The participants comprised of 334 high school 1st-graders. The results indicated that: (1) Girls showed higher levels of both narcissism and emotional self-disclosure than boys, but there was no gender difference evident in the levels of depression and happiness. (2) The more the students felt depressed, the less they experienced happiness. Additionally, the more the students disclosed emotionally about themselves, the less they experienced depression. (3) High levels of narcissism and low levels of emotional self-disclosure increased depression, but the interactional effect between narcissism and emotional self-disclosure on depression was not statistically significant for either gender. Moreover, low levels of narcissism and high levels of emotional self-disclosure tended to see increased levels of happiness for both genders, however the interactional effect between narcissism and emotional self-disclosure on happiness was statistically significant only for boys. That is, for boys, the negative effects of narcissism on happiness can be reduced if the level of emotional self-disclosure is high.