Background : The purpose of this study was to investigate the incidence of unplanned endotracheal extubation and to identify the influencing factor of unplanned extubation in ICUs for providing baseline data in developing prevention strategies and administrative standards. the medical records and hospital information system. In order to analyze factors related to unplanned extubation, the subjects of this study were divided by unplanned extubation group and planned extubation group and were matched by its sex, age, and disease groups in a ratio of one to two. The data were analyzed by descriptive statistics, ${\chi}^2$- test, t-test, Fisher's exact test, and logistic regression analysis with SPSSWIN 10.0 program. Result : 1) Forty-seven(4.99%) of 942 intubated patients experienced unplanned extubation 65 times during the twelve-month period. Thirtyfour( 72.34%) of 47 unplanned extubated patients required reintubation, whereas thirteen patients(27.66%) did not. 2) About half of unplanned extubation(46.8%) occurred during the night shift. 3) As for the nursing activity, respiratory nursing activity score(P=.0.06) and total nursing activity score(P=.011) showed statistically significant differences between unplanned extubation group and planned extubation group. 4) As for the patient status, unplanned extubation group showed more lower consciousness level(P=.000), more irritable or agitated behavior(P=.000), and had more applied physical restraints(P=.000) than planned extubation group. 5) As for the intubation related variables, unplanned extubation group revealed more intubated with respiratory failure(P=.000), more dependent on mechanical ventilation(P=.015) than planned extubation group. 6) Factors affecting unplanned extubations in intensive care unit patients were irritable or agitated behavior(odds ratio=13.757), night shift(odds ratio=7.166), and mechanical ventilation(odds ratio=6.257) from conditional logistic regression analysis. Conclusion : The most affecting factor of unplanned extubation was agitated or irritable behavior. Therefore the results of this study could be helpful to ICU nurses for meticulous care, decision making, timely intervention, and development of intervention strategies for preventing unplanned extubation.