Background The turnover of new and mid-career nurses has been increasing, leading to challenges in recruiting and retaining nursing staff. Objectives Securing and retaining mid-career nurses is crucial for ensuring high-quality care. However, little is known about mid-career nurses’ experiences regarding turnover. This study aimed to understand the experiences of mid-career nurses and identify strategies to enable mid-career nurses to maintain long-term employment in health services. Design Colaizzi’s phenomenological methodology was adopted to illuminate the subjective meaning derived from the work-related challenges of mid-career nurses, leading to turnover. Focus group interviews were conducted to delve into the work challenges faced by mid-career nurses. Method The participants were 23 mid-career nurses working in one tertiary hospital and six secondary hospitals across three Korean cities, recruited using purposive and snowball sampling. The inclusion criteria entailed a minimum of three years of nursing experience and current employment within a designated department or clinical area within the hospital environment, commonly known as a nursing unit. Such units encompassed a range of clinical settings, including medical-surgical units, intensive care units, and emergency rooms. The interview data were transcribed verbatim, and significant statements were extracted from abstract sentences to derive themes through an analytical process. Results Analysis of the work experiences of 23 mid-career nurses in medical institutions yielded 15 themes and 4 theme clusters derived from 353 meaningful statements. These theme collections were identified as ‘Difficulties endured as a mid-career nurse’, ‘Meaningless and regrettable new graduate nurses’ education’, ‘An inexpressibly poor work environment’, and ‘Systems and policies needed to remain in the hospital’. Conclusions Difficulties faced by mid-career nurses including the establishment of an education and career development system, provisions for guaranteed leave, a diverse and flexible work system, opportunities for effective communication, and engagement with the opinions of mid-career nurses should promptly be addressed.