Pneumonia is an inflamation of the lung parenchyma and transmitted through respiratory air. Malnutrition and environmental conditions that are not clean can increase risk of pneumonia. Pneumonia cases at Semarang in 2007 reached 3230 patients, an increase from 2006 amounted to 2286 patients. For malnutrition also tended to increase from 0,34% (1999) to 1,88% (2004). The purpose of this research is to determine malnutrition as a risk factor for incidence of Pneumonia in infants. Kind of research is the method of analytic observational with Cross Sectional study. The study was conducted at RSUD Kota Semarang. The data used are secondary data from the patient Medical Record, which were analyzed using Chi Square test with Risk Estimate to determine the prevalence ratios and confidence intervals.