Abstract: Objective To investigate the impacts of the heat wave on the emergency department (ED) visits among different ages, gender, illness groups in Beijing in 2010. Methods Daily maximum and mean temperatures in Beijing were obtained from the U.S. National Climatic Data Center website. The ED visit data were collected from a tertiary general hospital in Beijing. The heat wave period was defined from July 22 to 30, 2010 when the daily maximum temperature was higher than 35 ℃ for three or more consecutive days. The control period from July 23 to 31, 2009 was selected according to the same number of days in the same season and weeks without high temperature. The rate ratios (RRs) of ED visits during the heat wave and control period were calculated to determine the impact of heat wave on ED visits in different groups. Results The total ED visits in the study hospital during the heat wave were 1 567, increased 9.4% compared with those in the control period (1 433). An increased risk was observed for ED visits during the heat wave period compared with those in the control (RR=1.09, 95% CI: 1.05-1.13). The ED visits for children during the heat wave period were 434, increased 61.3% compared with those in the control period (269) (RR=1.61,95% CI：1.49-1.74). The ED visits for the elderly during the heat wave were 243, increased 25.9% compared with those in the control period (193) (RR=1.26,95% CI：1.14-1.39). The ED visits for respiratory diseases during the heat wave period were 497, increased 14.5% compared with those in the control period (434) (RR=1.15,95% CI：1.07-1.22). During the heat wave, the RR was 1.08 (95% CI：1.03-1.14) for males and 1.11 (95% CI：1.05-1.16) for females, increased for both gender groups compared with those in the control period. Conclusion The heat wave could increase the risk of ED visits and the sensitive groups might be the elderly, children and patients with respiratory diseases.