This study investigated the feasibility of conducting a randomized controlled trial to evaluate a self-management mobile app for bereaved adolescents. Key areas assessed were recruitment, randomization, data collection, and intervention acceptability. In an internal pilot trial - where a pilot phase is embedded within a main trial to assess its feasibility − 36 adolescents aged 12–19 were randomized to use the app or a website with psychoeducation. All adolescents had experienced the loss of a family member and completed assessments prior to receiving the intervention and eight weeks after access. Results revealed the trial to be feasible, although indicating the need for minor adjustments to recruitment, screening, and inclusion criteria. Adolescents reported high satisfaction with the app, highlighting its helpfulness in understanding grief, improving communication, and seeking support. Overall, the study supports the feasibility of proceeding to a main trial within which app helpfulness and effects can be further explored.