Purpose: The purpose of this study was to identify the mediating effect of professionalism in the relationship between clinical competence and field adaptation in newly graduated nurses. Methods: The participants in this study were 213 nurses from four tertiary hospitals who had less than 12 months of nursing experience. Data were collected during January and February, 2013. A structured questionnaire was used for data collection and data were analyzed using descriptive statistics, Pearson correlation coefficients, and path analysis with the SPSS/WIN 21.0 and AMOS 21.0 programs. Results: The mean score for clinical competence was $2.85{pm}0.25$, for professionalism, $3.10{pm}0.30$, and for field adaptation, $2.79{pm}0.37$. There was a significant positive relationship between clinical competence and field adaptation. Also, professionalism was positively correlated with field adaptation. Professionalism showed mediating effects between clinical competence and field adaptation. Improvement of clinical competence increased professionalism and the increased professionalism raised the field adaptation. Conclusion: Based on these findings, orientation programs including strategies to increase professionalism, should be established to promote effective field adaptation in newly graduated nurses. These orientation programs can strengthen professionalism, the mediator between clinical competence and field adaptation in newly graduated nurses.