Background: According to studies, despite the proven and effective role of mechanical ventilation on patients with respiratory failure, the positive effects of semi-upright position on oxygenation and ventilation of patients under mechanical ventilation and nurses’ training about them have been neglected. This study aimed to investigate the effect of outcome-based education of nurses on maintaining the semi-upright position in mechanically ventilated patients (MVPs). 
Methods: This study was an outcome-based research and designed with pretest/posttest. All nurses of intensive care unit of Firozgar Hospital participated in a 2-hour individual training course with the outcome-based approach on maintaining the semi-upright position in MPVs. The obtained data were collected by a checklist, including questions about demographics, knowledge, and performance. Assessment of the performance was performed via observation and completing checklist by the researcher. After collecting data, they were analyzed through descriptive and inferential statistics using SPSS V.20. 
Results: The results showed that the mean(SD) score of nurse’s knowledge before and after training were 47.41(23.63) and 89.63(10.18), respectively and administering semi-upright position in MVPs in the posttest was significantly increased.
Conclusion: The outcome-based education on maintaining the semi-upright position in MVPs has positive effects on knowledge and performance of nurses. We recommend use of this method in nurses’ curriculum.