Background:H1N1 influenza A, commonly known as swine flu, is a respiratory illness caused by the H1N1 influenza virus. The present study was conducted to assess adverse drug reaction profile of oseltamivir. Materials & Methods:84 suspected or confirmed cases of H1N1 influenza A, close contacts of cases H1N1 influenza A of both genders were enrolled. Oseltamivir was administered 75 mg twice a day for 5 days in group I (therapeutic) and 75 mg once a day for 10 days in group I (prophylactic). Causality assessment by Naranjo's scale was done. Results: In group Iand group II, adverse drug reactions were nausea in 25% and 22%, vomiting in 14% and 11%, gastritis in 19% and 11%, weakness in 32% and 19%, headache in 11% and 9%, abdominal pain in 7% and 2%, vertigo in 5% and 3% and urgency of micturition in 4% and 5% respectively. The difference was significant (P< 0.05). Adverse drug reaction by Naranjo's scale were possible and probable such as nausea14%and 11%, vomiting10% and 4%, gastritis8% and 11%, weakness13% and 12%, headache8% and 3%, abdominal pain7%, vertigo4% and 1% and urgency of micturition in 3% and 1% respectively. The difference was significant (P< 0.05). Conclusion: Oseltamivir is well tolerated; however, gastrointestinal adverse drug reactions (ADRs) are the most common and can be easily avoided by taking the medication with antacids and/or H2 receptor antagonists after a meal.