Pneumonia is a very common disease in children. However, clinical symptoms of pneunia in infants under 1 year was atypical. This study was carried out to describe the clinical features of pneumonia in 393 children under 1 year old with pneumonia at Respiratory Department of the National Hospital of Pediatrics from 01/01/2010 to 30/06/2010. Results showed that nearly half of children with pneumonia were seen in the group of 2 - 6 months (49.4 percent). Male/female was 2.1/1. The majority of first signs was cough (96.9 percent). 37.4 percent of hospitalized patients with very serious pneumonia and 52.9 percent with severe pneumonia. In infants under 2 months, severe symptoms such as wheezing, in drawing and cyanosis were seen more frequent than 2 other groups (p 0.05). Fever was frequently observed in the group children of 7 - 12 months (p 0.001). The percentage of children with level 2 and 3 malnutrition had very severe pneumonia and with high percentage (68.2 percent) with p 0.05. More younger children had more severe pneumonia, in the children less than 2 months the rate of very serious pneumonia was high 73.6 percent with p 0.001. In conclusion, in children of group less than 2 months old, pneumonia was more severely and more severe symptoms than others groups (p 0.001). Malnutrition status affected to the severity of the disease (p 0.05).