Many studies have examined the short-term effects of air pollution on frequency of daily mortality over the past two decades. However, information on the relationship between levels of fine particles (PM 2.5 ) and daily mortality is relatively sparse due to limited availability of monitoring data. Further the results are inconsistent. This study was undertaken to determine whether there was an association between PM 2.5 levels and daily mortality rate in Kaohsiung, Taiwan, a large industrial city with a tropical climate. Daily mortality rate, air pollution parameters, and weather data for Kaohsiung were obtained for the period from 2006 through 2008. The relative risk of daily mortality occurrence was estimated using a time-stratified case-crossover approach, controlling for (1) weather variables, (2) day of the week, (3) seasonality, and (4) long-term time trends. For the single-pollutant model (without adjustment for other pollutants), no significant effects were found between PM 2.5 and frequency of daily mortality on warm days (≥25°C). On cool days, PM 2.5 showed significant correlation with increased risk of mortality rate for all causes and circulatory diseases in single-pollutant model. There was no indication of an association between PM 2.5 and deaths due to respiratory diseases. The relationship appeared to be stronger on cool days. This study provided evidence of associations between short-term exposure to PM 2.5 and elevated risk of death for all cause and circulatory diseases.