Purpose: This study aimed to examine the experiences of nurses who worked with substitute nurses and to identify the essence and structure of these experiences. Methods: Fourteen nurses from three tertiary hospitals in Seoul, each operating an independent a substitute nurse system, participated. Data were collected through individual interviews conducted from January 10 to February 22, 2025. Data analysis was performed using Colaizzi’s phenomenological method. Results: The study's results were organized into 35 themes, 13 theme clusters, and 5 categories: ‘‘The inescapable nature of shift work without a substitute’’, ‘‘Various perspectives on the introduction of substitute nurses’’, ‘‘Positive changes brought by substitute nurses’’, ‘‘Limitations of substitute workforce operation and the gap with actual practice’’, and ‘‘The supplementation and expansion of staff nurse system are essential’’. Conclusion: The substitute nurse system effectively reduced care gaps and staff nurse burden, however, it also exposed significant challenges, including staffing shortages and insufficient preparation for substitute nurses. Participants emphasized the need for system improvements, such as increasing substitute nurses numbers, strengthening pre-deployment training, and adopting more flexible staffing models. Despite these challenges, participants expressed optimism about the system's potential to improve nurse well-being, enhance patient care quality, and support organizational development. This study provides essential data on nurses’ experiences with substitute nurses in tertiary hospitals, which can inform strategies for effective implementation and sustainability of the substitute nurse system in clinical practice, supporting its successful integration and long-term benefits for both nurses and patients.