We evaluated the reliability and validity of the Korean translation of the quality of oncology nursing care scale (K-QONCS) and verified its suitability as a tool to assess the quality of cancer patient care in Korea. To validate the content validity of the K-QONCS, five oncology nurse experts assessed the suitability of the adapted tools. Exploratory factor analysis (EFA) was used to assess construct, convergent, discriminant, and criterion validity. A survey of 235 adults aged > 18 years who had been diagnosed with cancer and were receiving treatment was conducted to validate the K-QONCS. The QONCS was translated and appropriately modified to reflect expert opinion, and its content validity was confirmed to be high through indicators such as item-level content validity index, scale-level content validity index using an averaging calculation (S-CVI/Ave), and S-CVI/universal agreement. Eight factors were derived by EFA; each factor reflected different aspects of quality of care. The scale exhibited convergent and discriminant validity, demonstrated by multitrait-multimethod matrix analysis and correlation analysis with the Nursing Satisfaction Scale. The Cronbach's alpha coefficient was 0.92, indicating high overall internal consistency. We demonstrated the reliability and feasibility of the K-QONCS. The K-QONCS may help oncology nurses to improve patient care experiences and outcomes as well as advance oncology nursing practices in South Korea.