Cyberbullying is a major issue facing adolescents in the digital age, with the use of social media and mobile applications that can negatively impact their mental and emotional health. The importance of cyberbullying prevention has become a major focus in various educational programmers to protect the well-being of adolescents. This research aims to develop a mobile application that facilitates ‘RASA’ character building to support cyberbullying prevention among adolescents. This research used the RnD research and development method with the ADDIE model (...) (Analysis, Design, Development, Implementation, Evaluation). The population of high school students of SMPN 2 Medan and SMPS Gajah Mada with sampling technique using purposive sampling technique. Data analysis techniques include descriptive analysis, validity test, normality test, homogeneity, reliability and reliability and paired sample t-Test test. Based on the results of the expert validity test, it shows that the character-building mobile application ‘RASA’ is said to be valid. This is evidenced by the average media expert validation of 91.3%, the average material expert validation of 88.7%, and the average learning design expert of 86.9%. As well as in the practicality test which resulted in a practicality level of 90.52%. This shows that the character-building mobile application ‘RASA’ is valid for the prevention of Adolescent Cyberbullying in adolescents. This mobile application can increase adolescents' awareness, acceptance, support, and action towards cyberbullying, thus creating a safer and healthier online environment. (shrink)