BACKGROUNDNurses' turnover intention has garnered significant global attention due to the shortage of the nursing workforce. New graduate nurses encounter challenges as they transition from students to professional nurses. Many new graduate nurses have experienced transition shock, which impacts their turnover intention. Researchers show that undergraduate readiness for practice is linked to transition shock and turnover intention, but there is a lack of longitudinal studies investigating their associations and causality.OBJECTIVESTo explore the longitudinal factors affecting turnover intention among new graduate nurses, as well as the mediating role of transition shock in the relationship between readiness for practice and turnover intention.DESIGNA retrospective longitudinal design.SETTINGSThis study was conducted in 54 nursing schools in South Korea.PARTICIPANTSA total of 232 new graduate nurses who participated in the New Nurse e-Cohort Panel Study as students and have continued working at the same hospital since graduation were included.METHODSSurveys were conducted during three periods: two months before graduation (T0), six months after graduation (T1), and one year after graduation (T2). Hayes' PROCESS macro Model 4 was utilized to analyze the mediating effect of transition shock (T1) on the relationship between readiness for practice (T0) and turnover intention (T2) among new graduate nurses.RESULTSReadiness for practice (β = -0.140, p = 0.028) and transition shock (β = 0.259, p < 0.001) were significantly associated with turnover intention. Transition shock acted as a mediator between readiness for practice and turnover intention (β = -0.165, 95 % confidence interval -0.311 to -0.051) among new graduate nurses after controlling for work experience, working in desired units, and completion of internship before nursing school graduation.CONCLUSIONSThis study explored the causal relationships among readiness for practice, transition shock, and turnover intention of new graduate nurses. The findings suggest that higher readiness for practice decreases transition shock and influences the intention to leave. To retain a valuable nursing workforce, nursing schools should strive to create a supportive learning environment that prepares students with a high level of readiness for practice. Additionally, hospitals' nursing managers and administrators should implement a structured adaptation program for new graduate nurses to facilitate a smooth transition into the profession.