Aims and Objective: To investigate the determinants of missed nursing care and to analyse the mediating effect of holistic nursing competence on the relationship between transition shock and missed nursing care. Background: Transition shock of newly graduated nurses is associated with missed nursing care. Previous studies have shown the determinants of missed nursing care among nurses, but little is known about the relationship between missed nursing care, transition shock and holistic nursing competence. Design: Descriptive and correlational design. Methods: The study was conducted among newly graduated nurses (n = 201) working in acute care hospitals for 1–12 months. The MISSCARE survey, Holistic Nursing Competence Scale and Nursing Transition Shock Scale were used for data collection, in addition to a sociodemographic question form. Data were analysed using Pearson correlation, multiple regression and mediation analyses. The study was reported following the STROBE checklist. Results: The determinants of missed nursing care among newly graduated nurses were sex, unit type, rotating shift work, holding a certificate, holistic nursing competence and transition shock. All these variables explain 35% of the variance in missed nursing care. Holistic nursing competence directly mediated 51.7% of the relationship between transition shock and missed nursing care. Conclusions: Holistic nursing competence may decrease missed nursing care by reducing the effects of transition shock on newly graduated nurses. Relevance to Clinical Practice: The study highlighted that newly graduated nurses are an important population regarding missed nursing care. The determinants of missed care should be considered in the nursing care delivery to prevent missed care by newly graduated nurses. Based on the study findings, some recommendations were made for nurse managers and faculty for the orientation program and undergraduate nursing education.