Abstract: Objective To analyze the impact of ambient PM2.5 on hospital outpatient visits for respi?ratory diseases. Methods Data on ambient PM2.5，PM10，SO2，NO2，CO，O3-1h and O3-8h in 2017 were collected from Foshan Meteorological Bureau and Foshan Environmental Protection Bureau. Data on daily hospital outpatient visits were collected from two hospitals in Foshan. A time?series analysis using a gener?alized additive model（GAM）was applied to assess the association between ambient PM2.5 concentration and hospital outpatient visits for respiratory diseases after adjustment for long ?term trend，day ?of ?week， meteorological factors and other air pollutants. Results Air pollution in Foshan City showed excellent lev?el as a whole in 2017. The main pollutants of PM2.5，PM10，SO2，NO2，CO，O3-1h，and O3-8h met the sec?ond or higher standards of the National Environmental Air Quality Standard（GB 3095-2012）. The aver?age PM2.5 concentration in Foshan in 2017 was 33.2 μg/ m3，meeting the national second ?level standard. The numbers of days exceeding the standard were 9 days all the year round. The total outpatient visits for respiratory diseases in the two hospitals were 261 158 with average 715.50 visits per day. The hospital dai?ly average outpatient visits for respiratory diseases were positively correlated with the air pollutants of SO2， NO2，and PM10 by the Spearman correlation analysis（R：0.19，0.33，0.20；P＜0.05 for all）. The GAM analysis showed that the daily average concentration of ambient PM2.5 was positively correlated with the hos?pital outpatient visits for respiratory diseases. The effect of ambient PM2.5 was the largest on lag 0 day（ER＝2.744；95% CI：0.701，4.827）. For every 10 μg/m3 increment of ambient PM2.5，the daily outpatient vis?its for respiratory diseases increased by 2.744%。 In the analysis of multi-pollutant model，when introduc?ing O3-1h（ER＝3.425；95% CI：1.278，5.617）and O3-8h（ER＝4.611；95% CI：2.373，6.899），their combined effect with PM2.5 made the correlation between PM2.5 and outpatient visits for respiratory diseases increased significantly. Conclusion The ambient PM2.5 concentration was positively associated with hospi?tal outpatient visits for respiratory diseases in Foshan City.