Abstract: In order to understand the contribution of fireworks to Beijing's gaseous pollutants and water-soluble inorganic ions in PM_2.5 during the Spring Festival, online data of PM₁₀, gaseous pollutants and water-soluble inorganic ions from February 1^st to March 1^st, 2011, were analyzed by comparing concentration characteristics and conducting correlation analysis. The results showed that fireworks aggravated the PM₁₀ pollution in a short time period. During the dense firework-setting-off period (i.e., New Year's Eve, Spring Festival, the 5^th day of the first lunar month and the Lantern Festival), hourly mass concentration of PM₁₀ (232 μg/m³) and volume fraction of SO₂ (40.2×10^-9) were 3.7 and 2.5 times more than their levels during normal days (63 μg/m³ and 16.0×10^-9), respectively. The ratios of the contribution of fireworks to PM₁₀ (hourly ρ) and SO₂ (hourly φ) were 56.8% and 35.6%, respectively. No significant impacts from fireworks on CO, NO or NO₂ were detected. The concentration of PM₁₀ and gaseous pollutants increased 3.0-8.3 times during the pollution caused by other factors in February 2011. Setting off fireworks had the greatest impacts on Mg²⁺, K⁺ and Cl^-, with contribution ratios 88.6%, 87.2% and 65.8%, which were higher than their levels during normal days (65.0 times, 31.6 times and 6.9 times, respectively). Mg²⁺, K⁺ and Cl^- showed a high correlation during the dense firework-setting-off period; the correlation coefficient between any two of these species was above 0.9. The concentrations of SO₄^2-, NO₃^- and NH₄⁺ significantly increased during the polluted period, being 3.8 times, 16.4 times and 8.3 times higher than their levels during normal days, respectively, which were also higher than their levels during the dense firework-setting-off period (2.7, 2.5 and 2.1 times respectively). During the firework-setting-off period, ions existed in the form of NH₄HSO₄, NH₄NO₃, KNO₃, KCl, NH₄Cl and MgCl₂ in PM_2.5, and the value of SOR was higher than in both normal days and the polluted period. The highest value of NOR appeared in the polluted period. The research showed that fireworks had the greatest impact on ρ(PM₁₀), ρ(Mg²⁺), ρ(K⁺) and ρ(Cl^-) in PM_2.5; during the polluted period, the ions' concentrations were significantly increased, and the higher value of NOR was responsible for the increasing of ρ(NO₃^-).