Purpose Air pollution is detrimental to health. PM2.5 is an air pollutant below 2.5µm in diameter, when inhaled directly into the lungs, plays an important role in the exacerbation and triggering of asthma while also stimulating the eyes and nose. Recent Chinese industrialization has caused an increase in air pollution crossing international borders, but research involving PM2.5 air pollution is not vast. This research investigates air pollution health effects on children suffering from bronchial asthma with a priority on PM2.5. Methods Children with bronchial asthma recorded peak flow meter, symptoms, and medications in a diary form at 23 medical institutions located in Western Japan. The period was during the winter season (December to March). Air pollution data was collected by the Ministry of Environment Government and local governments from monitoring stations nearest to the medical institutions. We assorted groups by medication use, accomplished GEE (generalized estimate equation) analysis by peak flow meter, and case-crossover analysis by symptoms. Results A total of 49 patients (22 male) were enrolled and 16 were put to use an asthma controller. There was no statistically significant association between peak flow and PM2.5 by GEE analysis with or without controller use. There was also no statistically significant association between PM2.5 and the symptoms of asthma, cough, nose, and respiratory infection medications but asthma reliever medication use was increased (OR 1.18, 95%CI 1.05-1.13). Conclusions PM2.5 concentration increment in a short-time period increased the risk of asthma reliever use in the winter season, but did not decline the peak flow, which was presumed by asthma controller use and air pollution forecast.