Lots of patients die while are waiting for organ transplantation because of organ shortage. ICU nurses play a major role in the different stages of the donation process. This study investigated the knowledge of ICU nurses about brain death. 126 ICU nurses from 36 hospitals filled out the questionnaire. Three scenarios were presented in a coma, brain death or in a persistent vegetative state (PVS). Respondents should be able to differentiate these three conditions, assess the patient status in each scenario in terms of dead or alive, and make a decision to inform the organ procurement system. 120 (%95.2), 100 (%79.4) and 104 (%82.5) recognized brain death, PVS and coma respectively. 55 (%43.7) and 56 (%44.4) believed that some one who was in vegetative state and coma respectively is dead. 90 (%71.4) believed that some one who was brain dead is alive. 3 (%2.4) didn’t consider to inform organ procurement about patient. Most of the ICU nurses didn’t believe that a brain dead patient is dead and this may effect on their cooperation with organ donation system.