East Asia currently has the largest SO2 and NO x emissions in the world. The long-range transport (LRT) of acidic pollutants in this region is of great concern but the extent is not well understood. Here results from combined long-term (⩾20 years) atmospheric deposition monitoring and air trajectory analysis in East Asia were reported. The results showed that despite the large decrease of SO2 and NO x emissions in Taiwan, annual deposition of non-sea-salt sulfate (nss- SO 4 2 − ) in northern Taiwan showed no decreasing trend during 1994-2020. However, when divided seasonally, both nss- SO 4 2 − and nitrate ( NO 3 − ) deposition had a significant decreasing trend in the summer but not in the winter. Similar patterns were found for Japan and Korea. Air trajectory models in combination with a regional emission map indicate that LRT from eastern China contributed up to 70% of the winter deposition of nss- SO 4 2 − and NO 3 − in Taiwan and up to 50% in Japan and Korea. The results indicate that LRT obscured the efficacy of local pollution control measures in East Asia and suggest that transboundary air pollution regulations are required to combat acid deposition.