Aims: To evaluate the effect of intravenous (IV) acetaminophen on reducing the need for morphine sulfate in intubated patients admitted to the Intensive Care Unit (ICU). Settings and Design: Current study was done as a clinical trial on the patients supported by mechanical ventilator. Subjects and Methods: Behavioral pain scale (BPS) scoring system was used to measure pain in the patients. All of the patients received 1 g, IV acetaminophen, every 6 h during the 1 ^st and 3 ^rd days of admission and placebo during the 2 ^nd and 4 ^th days. Total dose of morphine sulfate needed, its complications, and the BPS scores at the end of every 6 h interval were compared. Results: Totally forty patients were enrolled. The mean pain scores were significantly lower in the 2 ^nd and 4 ^th days (4.33 and 3.66, respectively; mean: 4.0) in which the patients had received just morphine sulfate compared to the 1 ^st and 3 ^rd days (7.36 and 3.93, respectively; mean: 5.65) in which the patients had received acetaminophen in addition to morphine sulfate too (P < 0.001). Cumulative dose of morphine sulfate used, was significantly higher in the 1 ^st and 3 ^rd days (8.92 and 3.15 mg, respectively; 12.07 mg in total) compared to the 2 ^nd and 4 ^th days (6.47 mg and 3.22 mg, respectively; 9.7 mg in total) (P = 0.035). Conclusion: In our study, IV acetaminophen had no effect on decreasing the BPSs and need of morphine sulfate in intubated patients admitted to ICU.