Recent papers have reported that Asian dust events have been associated with increased risks of all-cause mortality and rates of respiratory illness. The current study was designed to estimate the relative risk of mortality associated with Asian dust events. We used the daily counts of non-accidental deaths, air pollution and meteorological data in Seoul, Korea from 2000 to 2004. We divided all days during the study period into two groups according to the presence or absence of Asian dust events. For each group, we conducted time-series analysis to estimate the relative risk of total non-accidental death when the concentration of each air pollutant increased by the inter-quartile range (IQR). The average concentrations of every air pollutant on the days without a dust event were lower than those on the days with such an event. We found that the effect sizes of air pollution on daily death rates in the model without Asian dust events were larger than those in the model with Asian dust events, and were statistically significant for all air pollutants (PM(10), CO, NO(2), and SO(2)) except for O(3). Our results suggest that we are likely to underestimate the risk of urban air particles if we analyze the effect size of air pollution on daily mortality during Asian dust events. We hypothesize that the real health effect is much larger than previous results suggested.