We evaluated the dynamics of clinical symptoms of 2009 pandemic influenza A (H1N1) using a four-point scale sheet. The most frequent symptoms were fever and cough. The sum of symptom score was high during the first 4 days. Systemic symptoms peaked earlier, by day 2, and resolved faster than upper respiratory symptoms and lower respiratory symptoms after oseltamivir treatment. The lower respiratory symptoms resolved slowly over 2 weeks. The 2009 pandemic influenza A (H1N1) virus might involve primarily lower respiratory tract and could be the main cause of pneumonia.