Training programs are measures for providing nurses with theoretical and practical information needed for acquiring new skills and to continually improve their nursing practice . The aim of this study was to evaluate the effect of training program on nurses performance regarding care for patients under mechanical ventilator in intensive care units (ICUs) . Research hypothesis 1-Implementing of training program affect positively on post -test nurses knowledge scores regarding care for patients under mechanical ventilator in intensive care units compared with pretest. 2-Implementing of training program affect positively on post- test nurses practice scores regarding care for patients under mechanical ventilator in intensive care units compared with pretest . A quasi-experimental research design was utilized to conduct the aim of this study. This study was conducted in ICUs at Benha University Hospital.