Abstract: Objective To estimate the air pollutant PM2.5 related excess mortality risk assessment in Beijing during 17-31 January 2013 when serious haze weather attacked. Methods The exposure-response coefficient of PM2.5 on population mortality during 2008-2011 was calculated by using a time series analysis model. The PM2.5 related excess mortality risk in Beijing during 17-31 January 2013 was estimated by using a proportional risk model, the result was compared with that during the same periods from 2008 to 2011. Results An increase of 10 g/m3 of PM2.5 concentration in air could cause an increase of 0.28% of the overall mortality risk (95% CI:0.18%-0.41%), an increase 0.32% and 0.31% of cardio-cerebro-vascular disease(95% CI:0.16%-0.47%)and respiratory disease(95% CI:0.01%-0.63%)respectively. The PM2.5 related excess mortality risk was 164 persons/15 days in Beijing during January 2013 when serious haze weather attacked, which was significantly higher that during the same periods from 2008 to 2011 (57 persons/15 days) (2=51.800,P 0.01). The PM2.5 related excess mortality risk was high in Chaoyang and Haidian districts. Conclusion Cardio-cerebro-vascular disease and respiratory disease are prone to occur due to serious air population weather. PM2.5 could increase the excess mortality risk in population, which could be high in urban area with dense population.