Although the relationship between asthma and exposure to fine particulate matter (PM2.5) has been frequently measured, reported conclusions have not been consistent. As emergency department (ED) visits are an effective way to estimate health outcomes for people with asthma and short-term exposure to PM2.5, this review systematically searched five databases without language or geographical restrictions from inception to January 13, 2015 to study the impact of PM2.5 on asthma ED visits. A random-effects model was used to calculate the pooled risk ratio (RR) and 95 % confidence intervals (CI). With respect to short-term effects, asthma ED visits increased at higher PM2.5 concentrations (RR 1.5 % per 10 mu g/m(3); 95 % CI 1.2-1.7 %), and children were more susceptible (3.6 % per 10 mu g/m(3); 95 % CI 1.8, 5.3 %) than adults (1.7, 95 % CI 0.7 %, 2.8 %) to increased PM2.5; the ED visits increased during the warm season by 3.7 % (95 % CI 0.5, 6.9 %) per 10 mu g/m(3) increase in PM2.5, which was higher than the corresponding increase during the cold season (2.6, 95 % CI 0.7-4.6 %). This demonstrates that ambient PM2.5 has an adverse impact on asthma ED visits after short-term exposure and that children are a high-risk population when PM2.5 concentrations are high, particularly in warm seasons, during which measures should be taken to prevent PM2.5.