Abstract: Objective To investigate the effect of ambient particulate matters with aerodynamic diameter ≤ 2.5 μm (PM_2.5) and ≤ 10 μm (PM₁₀)on the incidence of influenza-like illness in Ningbo.Methods Time series study on PM_2.5, PM₁₀ and the incidence of influenza-like illness from 2014 to 2016 was investigated by using the distributed lag non-linear model (DLNM). The corresponding attributable risk proportion(AR%) was calculated to assess the acute effect of contaminants on the onset of influenza-like illness.Results There was a positive correlation between the two kinds of particulate matters, PM₁₀ and PM_2.5, and the incidence of influenza-like cases. Analysis of single pollutant showed that both PM₁₀ and PM_2.5 increased the incidence of influenza-like illness in the short term, and the effect was characterized by hysteresis and harvesting, with the AR% of 5.13%(95% CI:2.94%-7.37%,P<0.001) and 2.52%(95% CI:-0.75%-5.90%,P=0.139), respectively. Furthermore, the acute health effects caused by PM₁₀ were more severe than that caused by PM_2.5. Analysis of double pollutants showed that the association between PM₁₀ and influenza-like illness was changed after adjusting for other gaseous pollutants. By contrast, PM_2.5 significantly increased the incidence of influenza-like illness with a 0-7 day lag after adjusting nitrogen dioxide (NO₂).Conclusion Increased concentrations of PM₁₀ and PM_2.5 may increase the incidence of influenza-like illness.