The purpose of this study was to measure the decrease in depression symptoms experienced by the participant before and after following the intervention by applying the Internet-based Cognitive Behavior Therapy (iCBT) approach. The participant was HN, a 14-year-old female adolescent who refused school due to major depressive disorder. The design of this study was a single-subject design with pre-post measurement. The intervention program was held eight sessions with a pre-session one day before, and a follow-up session was given two weeks after. The instruments used for this research are Beck Depression Inventory-II (BDI-II) to measure depression symptoms and Mood-o-meter, which serves as a mood rating to measure HN's mood fluctuation. This study showed depression symptoms decreased and positive mindset change and behavior towards the social environment at the end of the intervention program.