Study aim: To evaluate the effect of a transtheoretical model-based educational intervention on self-care in adults with chronic obstructive pulmonary disease (COPD). Design: Randomized, parallel-group, controlled clinical trial with two study arms (intervention and control). A total of 40 participants will be randomly allocated to the intervention and control groups in a 1:1 ratio using a random number table. Settings and conduct: The study will be conducted at Khatam al-Anbia Hospital in Abarkooh. A total of 40 eligible participants will be recruited through convenience sampling and randomly allocated to the intervention and control groups (20 participants per group) in a 1:1 ratio using a random number table. Outcomes will be assessed at baseline, immediately after the intervention, and at 3-month follow-up. Participants/Inclusion and exclusion criteria: Inclusion criteria: Adults with confirmed COPD, in the precontemplation, contemplation, or preparation stage of behavior change, able to provide written informed consent, and without asthma, pneumonia, active malignancy, or immunodeficiency. Exclusion criteria: Development of dementia, uncontrolled psychiatric or serious cardiopulmonary disease during the study, or withdrawal of informed consent. Intervention groups: Intervention group: Participants will receive a transtheoretical model (TTM)-based educational intervention according to their stage of behavior change (precontemplation, contemplation, preparation, action, and maintenance). The intervention will be delivered through face-to-face training sessions lasting 45–60 minutes. Control group: Participants will receive routine care without the TTM-based educational intervention during the study period. Main outcome variables: Self-care status Stage of behavior change Self-efficacy