This study quantified the uncertainties in concentrations and direct radiative forcing of anthropogenic aerosols due to emissions in eastern China using a global chemistry–aerosol–climate model. The emission inventories included three global inventories, ACCMIP (Atmospheric Chemistry & Climate Model Intercomparison Project), EDGAR-HTAP (Emission Database for Global Atmospheric Research for Hemispheric Transport of Air Pollution), and EDGAR Version 4.2, and one regional INTEX-B (Intercontinental Chemical Transport Experiment—Phase B) inventory. The uncertainties (a percentage of the standard deviation divided by the mean value across the four inventories) in the regional surface-layer aerosol concentrations due to emissions were 3.9% in sulfate, 40.0% in nitrate, 18.4% in ammonium, 11.1% in POA, 16.7% in SOA and 15.4% in BC. Compared with the ACCMIP model results based on a uniform emission inventory, the impacts of emissions were smaller. One exception is the regional surface-layer nitrate concentration, which had comparable uncertainties due to the emissions (40.0%) and the models (43.8%) because of the complex nitrate chemistry and the highly uncertain NH3 emission. The mean regional aerosol direct forcing at the top of the atmosphere between 1850 and 2006 was −3.6Wm−2 under all-sky conditions and was enhanced up to −3.83Wm−2 after the model assimilated the MODIS find-mode aerosol optical depth (AOD). The impact of the assimilation of absorption AOD is discussed. The uncertainties in aerosol direct forcing were smaller than those of the ACCMIP inter-model results, but still significant. An accurate emission inventory is essential for quantifying the role of aerosols in regional climate.