Background: In Indonesia, pneumonia is the second leading cause of death after diarrhea, with estimated mortality rate at 15.5% (Depkes RI, 2005). Whereas in Yogyakarta there are 10% cases of pneumonia in infants of 1937 numbers of infants. Pneumonia is a disease caused by viruses and bacteria that are influenced by several risk factors among which are nonexclusive breastfeeding and exposure to tobacco smoke. The purpose of this study is to determine different effect between nonexclusive breastfeeding and tobacco smoke exposure in case of pneumonia of infants aged 6 months to 2 years in Yogyakarta. Methods: Analytic observational study with case control approach conducted on 160 samples consisting of 80 case samples and 80 controls were taken by purposive sampling. Samples were matched by age and sex between case samples and controls to minimize confounding factors. This research was conducted in three hospitals in Yogyakarta. Data collected by held guided interview to mothers using questionnaires and viewed medical records. Results: This study obtained significant relation between exclusive breastfeeding and pneumonia cases in children aged 6 months to 2 years in Yogyakarta with p-value < 0.001 and OR = 5.43 (95% CI = 0.093 – 0.361) which means infant with nonexclusive breastfeeding is 5.43 times riskier to have pneumonia than that with exclusive breastfeeding. While for tobacco smoke exposure variables, obtained no significant relation with pneumonia in infants aged 6 months to 2 years in Yogyakarta with p-value = 0, 423 and OR = 1.287 (95% CI = 0.690 to 2.401). Conclusion: There is a significant relation between exclusive breastfeeding and the risk of pneumonia in infant aged 6 months to 2 years with p-value < 0,05 and OR = 5.43. While between tobacco smoke exposure and pneumonia in children aged 6 months to 2 years do not have a significant relation with p-value > 0.05.