Objectives: Although a number of epidemiologic studies have examined the association between air pollution and mortality, data limitations have resulted in fewer studies of particulate matter with an aerodynamic diameter of ${leq}2.5{mu}m$ ($PM_{2.5}$). We conducted a time-series study of the acute effects of particulate matter with an aerodynamic diameter of ${leq}10{mu}m$($PM_{10}$) and $PM_{2.5}$ on the increased risk of death for all causes and cardiovascular mortality in Seoul, Korea from 2006 to 2010. Methods: We applied the generalized additive model (GAM) with penalized splines, adjusting for time, day of week, holiday, temperature, and relative humidity in order to investigate the association between risk of mortality and particulate matter. Results: We found that $PM_{10}$ and $PM_{2.5}$ were associated with an increased risk of mortality for all causes and of cardiovascular mortality in Seoul. A $10{mu}g/m^3$ increase in the concentration of $PM_{10}$ corresponded to 0.44% (95% Confidence Interval [CI]: 0.25-0.63%), and 0.95% (95% CI: 0.16-1.73%) increase of all causes and of cardiovascular mortality. A $10{mu}g/m^3$ increase in the concentration of $PM_{2.5}$ corresponded to 0.76% (95% CI: 0.40-1.12%), and 1.63% (95% CI: 0.89-2.37%) increase of all causes and cardiovascular mortality. Conclusion: We conclude that $PM_{10}$ and $PM_{2.5}$ have an adverse effect on population health and that this strengthens the rationale for further limiting levels of $PM_{10}$ and $PM_{2.5}$ in Seoul.