Abstract: ObjectiveTo explore the effect of ambient air pollution on hospital admissions of circulatory system diseases.MethodsThe data on air pollution index(API),meteorology and the hospitalization of circulatory system diseases from Jan 1st 2004 through Oct 31st 2007 in Lanzhou city were collected.The effect of the ambient air pollution on the health of circulatory system was investigated using generalized additive Poisson models after controlling for the effect of long term time trend,week and meteorology,and stratified by sex,age and the type of circulatory system diseaseses.ResultsThe every one inter quartile(48 units)increase in daily API was associated approximately with 1.35% to 3.62% increase of daily hospital admission for circulatory system disease for the delay range from current day to day 5 after the lag effect.The relative risk(RR)reachedits highest(1.04226,95% confidence intervalCI=1.02510-1.05881)among males five day after the lag effect.The RR for the females was higher than that of the males only in the four day after the lag effect.From current day to day 5 after the lag effect, the RR leve lwas high than 1.02 for the subjects over 65 years old.And the RR level by day 2 to day 5 after the lag effect for the subjects of 16 to 64 years old was of statistical significance.Ambient air pollution was more likely to affect hypertension patients and blood vessel of brain disease and the RR level reached its highest (1.07291,95%CI=1.04448-1.10211 and 1.04372,95%CI=1.01432-1.07397)at day 5 after the lag effect.The RR reached its highest(1.02521,95%CI=1.00157-1.04941)among coronary disease day 2 after the lag effect.ConclusionThe results show that air pollution considerably affects the circulatory system morbidity among urban residents,and the effects are related to gender,age and the type of circulatory system diseases.