Solitary confinement is the most severe disciplinary sanction in Indonesian correctional institutions and is imposed on inmates who commit serious violations of prison rules. Although it is intended to create a deterrent effect, isolation cuts off social interaction, restricts activity, and can place heavy psychological pressure on inmates. This study aims to analyse the dynamics of stress experienced by inmates serving solitary confinement at Class IIA Pekanbaru Correctional Institution and to identify the coping strategies they use. A qualitative approach with a case study design was employed. Data were collected through semi-structured interviews, unstructured observation, and documentation involving six informants: the Head of the Correctional Security Unit, a block security officer, a prison nurse, and three inmates who had served solitary confinement. The data were analysed using the interactive model of Miles, Huberman, and SaldaƱa and interpreted through Lazarus and Folkman's transactional theory of stress and coping. The results show that stress develops in stages. In the first days, inmates appraise isolation as a threat and experience pressure, disappointment, anger, fear, loneliness, sleeping difficulties, and worry about their families. Over time, they reappraise the sanction as a consequence of their own actions and an opportunity for self-improvement. Inmates cope through problem-focused coping, namely complying with rules, controlling behaviour, keeping simple routines, and maintaining physical health, and more dominantly through emotion-focused coping, namely prayer and worship, self-acceptance, thought control, positive reappraisal, and emotional release. These efforts are supported by coping resources from family, officers, and health workers. Disciplinary isolation should therefore be accompanied by routine psychological monitoring.