Managing postoperative pain require good understanding of the bio-ethical principles in order to preserve patients' rights. Bio-ethical principles in health care include autonomy, beneficence, justice and nonmaleficence. It is important that health care professionals understand that patients in pain have the right to satisfactory management. Good insight on ethical principles and how they relate to pain management places the nurse on a better pedestal to manage postoperative pain effectively. However, there is scanty literature on the level of Ghanaian nurses' knowledge and application of bio-ethical principles in postoperative pain management. Therefore, the study objectives were to: explore nurses' understanding of the bio-ethical principles in postoperative pain management; explore how nurses apply bioethical principles in postoperative pain management. The study employed qualitative exploratory descriptive design. Purposive sampling technique was used to recruit participants from the surgical wards. Semi-structured interview guide was designed for data collection. Data saturation was reached at the fourteenth participant. Thematic analysis method was used and themes emerged inductively. Three main themes identified through inductive content analysis of data were: beneficence, autonomy and justice. Findings showed that nurses had some appreciable level of knowledge of the fundamental principles related to ethics and applied them in postoperative pain management. Nurses knew their duties in advocating for patients. Patients rights to refuse treatment was also appreciated by some nurses. Nurses also demonstrated humanity by helping patients financially to settle hospital debts which explicitly shows the empathetic characteristics of nurses. The study concluded that nurses are knowledgeable in bioethical principles underpinning post operative pain management and also applied these principles when caring for surgical patients.