South Africa has the highest burden of adolescents living with HIV (ALHIV) in the world. The transition from pediatric to adult centered HIV care is a vulnerable period during which many clinical outcomes of ALHIV suffer. Transition readiness assessments may help ALHIV transition from pediatric to adult care to improve their health outcomes. Here, we evaluated the perceived acceptability and feasibility of a mobile health (mHealth) application, eHARTS, to determine transition readiness for ALHIV in South Africa. We conducted in-depth interviews with adolescents (n = 15) and healthcare providers (n = 15) at three government-supported hospitals in KwaZulu-Natal, South Africa. We used a semi-structured interview guide comprising of open-ended questions based on the unified theory of acceptance and use of technology. We did a thematic analysis of the data using an iterative, team-based coding approach to develop themes that were representative of the participants’ perspectives on the acceptability and feasibility of eHARTS. We found that most participants found eHARTS to be acceptable because of its simplicity and lack of stigma. Participants believed eHARTS was feasible as it could easily be administered within a hospital setting and integrated into regular clinic activity without disrupting patient care. Additionally, eHARTS was found to have great utility for adolescents and healthcare providers. Clinicians saw it as a valuable tool to engage adolescents and prepare them for transition. Despite concerns that eHARTS may give adolescents a wrong impression about immediate transition, participants suggested that eHARTS be framed in an empowering way as they prepare for transition to adult care. Our data showed that eHARTS is a simple, mobile transition assessment tool with perceived acceptability and feasibility for use in HIV clinics in South Africa for ALHIV. It is particularly useful for ALHIV and transitioning to adult care as it can help identify gaps in readiness for transition.