Purpose: The purpose of this study was to determine the concept of critical thinking and clinical reasoning and to propose a strategy to improve clinical reasoning for oncology nurses. Methods: A literature review was used. The concept of clinical reasoning and critical thinking in nursing was reviewed. Results of research of its area in Korea was evaluated. Results: A summary of the literature review for critical thinking, clinical reasoning, and research of critical thinking in clinical nurse in Korea was described. The concept of clinical reasoning was not established in nursing and thirteen articles were reported from 2000 to 2014 in Korea. Conclusion: Several strategies to improve the clinical reasoning in oncology nursing setting were proposed. First, personal effort to develop thought ability by using good questions. Second, nursing administration should offer support to the oncology unit to relieve the burden and to change the nursing delivery system to fit the oncology unit. Finally, nursing school has to teach teach critical thinking in the junior grade and develop clinical reasoning ability in the senior grade of clinical practice. it is necessary to teach not only the right practices but also the right questions and reasoned thinking to novice nurses during training by preceptors.