This work aimed to study the frequency of colonization of intubated ICU patients in Benha university hospital by anaerobic bacteria and their role in acquired ventilation associated pneumonia . this study was done on 35 patients (14 males and 21 female) admitted to ICU of Benha university hospital from December 2009 to September 2010, two tracheal aspirate samples were taken from each patients using sterile disposable mucus extractor direct smear , gram staining and anaerobic culture on Robertson cooked meat media for 24-48hr subculture were made on selective blood agars and identification of anaerobic bacteria species by RapID –ANA II system then antibiogram was made for isolated bacteria.