Purpose: The purpose of this study was to identify related factors of perceived delirium assessment ability (PDAA) of clinical nurses. Methods: A descriptive survey design with a convenience sampling was used with 266 nurses who were recruited from P university hospital. Data were analyzed using descriptive statistics, ANOVA, Pearson correlation, and stepwise multiple regression with the SPSS/WIN 18.0 program. Results: Nurses scored low for knowledge of symptoms and management of delirium. Factors related to PDAA were ‘sufficiency in opportunities for education about delirium’ (β=.325, p<.001), ‘experience of caring for patients with delirium’ (β=.228, p<.001), ‘duration of work’ (β=.139, p = .004), and ‘level of knowledge on delirium’ (β=.128, p = .021). These variables explained 24.2% of the variance in PDAA. Conclusion: Findings of the study indicate that nurses need up-to-date educational programs that include actual practices of delirium assessment as well as global knowledge of delirium. Because most nursing floors do not have care manuals for patients with delirium, having care manuals and corresponding educations is essential. Further studies including participants from broader geographical areas and methodology to examine the effects of educational program on PDAA are warranted to enhance the generalizability of the findings and examine the effectiveness of the program.