Aerosol physical and chemical properties and relative humidity (RH) in the marine atmosphere undergo their modifications under the influence of continentally polluted air mass. Effects of continentally polluted air mass on aerosol optical properties over the East China Sea were studied by using data of aerosol size and number, aerosol composition, and RH. These data were obtained under Atmospheric Particulate Environmental Change Experiment 2/Asian Pacific Regional Aerosol Characterization Experiment (APEX-E2/ACE-Asia). Data collected on 18, 21, 23, and 26 April 2001 were used in this study. In order to evaluate contributions of such modifications to aerosol optical thickness (AOT) and single scattering albedo (SSA), AOT and SSA of the continentally polluted marine atmospheres were compared with values calculated by replacing each parameter (aerosol composition, aerosol size and number, and RH) of the continentally polluted marine atmospheres with that of the marine atmosphere. Further, by not separating aerosol composition and aerosol size and number parameters, investigations were performed by replacing these parameters of the continentally polluted marine atmospheres with those of the marine atmosphere. Modification of aerosol size and number was found to have a tendency to increase AOT significantly, whereas modification of aerosol composition by only a few percentages. Since continental air had relatively low RHs, modification of RH was found to have a tendency to decrease the value. The result also suggested that the decrease of aerosol hygroscopicity by continentally polluted air mass tended to decrease AOT. On the other hand, not only aerosol composition and RH modifications, but also aerosol size and number modification had a tendency to decrease SSA. The study pointed out an important role of continentally polluted air mass on aerosol radiative forcing, due to the increase of AOT and the decrease of SSA over the East China Sea.