Pneumonia is an inflammatory condition of the lungs caused by infection, which may be triggered and exacerbated by particulate matter (PM) exposure. We aimed to estimate the effect of PM on emergency department (ED) visits in pneumonia patients with septicemia after controlling for gaseous pollutants. Measurements on PM2.5, PM10, and other air pollutants at each of the 11 air-quality monitoring stations in Kaohsiung City, Taiwan, were collected between 2007 and 2013. The medical records of non-trauma patients who were over 17 years old and had visited the ED with a principal diagnosis of pneumonia were extracted. Poisson models were used to examine the relationship between air pollutants and daily ED visits for pneumonia with septicemia. Interquartile increments in the levels of PM2.5, PM10, and NO2 at lag 0 were associated with increments of 25.5%, 21.61%, and 21.97%, respectively, in the number of ED visits for pneumonia with septicemia during the warm season. The effect estimates of PM2.5 were robust after adjusting for PM10 and NO2 in the two-pollutant model. PM2.5 had stronger associations with ED visits in the cases of pneumonia with septicemia in relatively healthy patients, such as those without comorbid hypertension, diabetes, stroke, liver cirrhosis, respiratory disease, or malignancy. In conclusion, although the existing evidence already supports a causal relationship between PM2.5 and pulmonary dysfunction, we propose that PM2.5 may also play an important role in emergency visits for pneumonia with septicemia during the warm season in southern Taiwan after adjusting for PM10 and NO2, especially among relatively healthy residents.