The effect of dust aerosols on the water clouds in East Asia was investigated by using satellite data and atmospheric chemical transport model. Water clouds were classified into cloud mixed with dust and cloud without dust, based on the brightness temperature difference between 11μm and 12μm channels observed from space by Moderate Resolution Imaging Spectroradiometer (MODIS). Cloud microphysical properties were analyzed by using cloud data and simulation results of aerosols obtained from an atmospheric chemical transport model. It was shown that the effective radius of cloud particles is smaller in the cloud including dust than that in the cloud without dust. On the other hand, an increase in sulfate aerosol concentration did not affect the cloud microphysical properties in this region, which suggests that the indirect effect by sulfate is saturated and dust aerosols act as cloud condensation nuclei in polluted air conditions.