In 2003, Shanghai recorded the hottest summer in over 50years. We investigated the impact on the mortality of a heat wave in 2003 in Shanghai. We calculated excess mortality and rate ratios (RRs) during the heat wave (July 19-August 6, 2003) compared to a reference (non-heatwave) period (June 28-July 9, and August 16-August 22). During the heat wave, the RR of total mortality was 1.13 (95% CI: 1.06-1.20), and the impact was greatest for cardiovascular (RREuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)1.19, 95% CI: 1.08-1.32) and respiratory (RREuro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin)1.23, 95% CI: 1.02-1.48) mortality. Gender did not make a statistically significant difference for the heat-wave impact. Elderly people (over 65years) were most vulnerable to the heat wave. Our analysis showed that the 2003 heat wave had a substantial effect on mortality in Shanghai. Public health programs should be implemented to prevent heat wave-related health problems in the city.