Background : This study aimed at identifying the effect of the standardized protocol on lowering the incidence of the ventilator associated pneumonia(VAP). Methods : The standard protocol focusing on decreasing VAP was made and applied at 5 ICUs (Medical ICU, surgical ICU, Respiratory ICU, Neonatal ICU, Pediatric ICU) in a university affiliated tertiary hospital, from April 1, 2000 to Oct 31, 2000. The protocol involved 3 parts : hand washing, the suctioning method and ventilator circuit management. All the nursing personnel received intensive education which was consisted of lecture, video film and demonstration. 176 nurses reported the performance of handwashing pre and post intervention. And randomly selected 15 nurses were observed by charge nurse and the handwashing practice was analyzed pre and post intervention. The incidence of VAP was compared with the former year incidence. Results : The self reported frequency of hand washing increased. In the direct observation of handwashing, the frequency, time, thoroughness of hand washing during 8 hours day duty was found to be improved. The frequency was increased from 1.1 time to 4.1 times; the time was improved from 1.7 seconds to 5.7 seconds and the thoroughness of the washing practice was from 0.2 times to 3.0 times respectively (p<0.001). The incidence of VAP decreased from at a rate of 15.63 number of case per 1,000 ventilator-day (April 1~August 31, 1999) to 7.23 number of case per 1,000 ventilator-days(April 1~Oct 31, 2000)(P<0.001). Conclusion : We developed the protocols which included hand washing, the suctioning method, and ventilator circuit management. Through the implementation of the protocol, the performance of hand washing improved and the VAP incidence rate in ICU was decreased.