Many risk factors related to HAP after abdominal operation admitted at ICU consisted of age > 60 years old, hypertension, chronic obstructive pulmonary disease, liver failure, cardiac failure, renal failure, diabetes, emergency operation, operation > 2 times, tracheal intubation, repeat tracheal intubation, mechanical ventilation, tracheotomy, gastric intubation, sputum aspiration, and sedative use significantly (p<0.05).