Segregation and radioactive analysis of aerosols according to their aerodynamic size were performed in France, Austria, the Czech Republic, Poland, Germany and Greece, after the arrival of contaminated air masses following the nuclear accident at the Fukushima Dai-ichi nuclear power plant in March 2011. On the whole and regardless of the location, the highest activity levels correspond either to the finest particle fraction or to the just upper size class. Regarding anthropogenic radionuclides, the Activity Median Aerodynamic Diameter (AMAD) were ranging between 0.25 and 0.71 µm for 137Cs; from 0.17 to 0.69 µm for 134Cs and from 0.30 to 0.53 µm for 131I, thus in the "accumulation mode" of the ambient aerosol (0.1 to 1 µm). AMAD noticed for the naturally occurring radionuclides 7Be and 210Pb ranged from 0.20 to 0.53 µm and 0.29 to 0.52 µm, respectively. Regarding spatial variations, AMAD do not show large differences from place to place compared with what was observed concerning bulk airborne levels registered on the European scale. When air masses arrived in Europe AMAD for 131I were about half those for cesium isotopes. Higher AMAD for cesium probably results from higher AMAD observed at the early stage of the accident in Japan. Lower AMAD for 131I can be explained by the adsorption of gaseous iodine on particles of all sizes met during transport especially small particles. Additionally, weathering conditions (rain) encountered during transport and in Europe in March and April contributed to the equilibrium of the gaseous to total 131I ratio. AMAD slightly increased with time for 131I whereas a clear decreasing trend was observed with the AMADs for 137Cs and 134Cs. On average, the associated Geometric Standard Deviation (GSD) appeared to be higher for iodine than for cesium isotopes. These statements also bear out a gaseous 131I transfer on ambient particles of a broad size range during transport. Highest weighted activity levels were found on the 0.49-0.95 µm and on the 0.18-0.36 µm size ranges, in France and in Poland, respectively. The contribution from resuspension of old deposited 137Cs was assessed for the coarse particle fractions only for the first sampling week.