Poor decision making among clinicians to transferring human immune deficiency virus (HIV) patients into second-line antiretroviral therapy (ART) has led to an increase in morbidity and mortality to people living with HIV (PLHIV). No clear barriers are known for clinicians not switching their patients. This is a descriptive qualitative research aimed to discover obstacles that influence clinicians' decision making to transferring patients into second-line ART despite higher level resistance to first-line ART. The researcher applied a participatory action research framework to solve the identified barriers with clinicians. Using the research questions the researcher explored reasons, perceived barriers and enabling factors for clinicians delay in making decision to transferring HIV patients into second-line ART. In-depth semistructured interviews were conducted with 30 participants. Six thematic areas (a) clinicians' capacity to diagnose treatment failure, (b) laboratory investigations, (c) availability, access, and tolerability to second-line ART, (d) clinicians' perceptions on ARV medicines, (e) clients' readiness for ARV medicines, and (f) adherence and retention to ARV medicines were analysed using STATA. Readiness, adherence and retention to ART, knowledge, competence and experience on ART , lack of viral load testing, and shortage of second-line ART were the common major barriers for clinicians in determining transferring patients into second-line ART. The government of Tanzania should acknowledge and create participation, responsibility, and commitment strategies to reduce the observed barriers. Findings of this study generates knowledge and provide actionable plans to help clinicians easily identify HIV patients who are in need of second-line ART.