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A decadal change in the frequency of dust outbreaks for April over East Asia using World Meteorological Organization (WMO) synoptic data was identified. The causes of the decadal change can be defined in terms of aeolian erosivity (i.e., ability of wind to cause erosion represented by wind speed) and erodibility (i.e., susceptibility of soil and land surface to wind erosion represented by the threshold wind speed for dust outbreak). Dust outbreak frequency (f(DO)) increased at many stations in Mongolia, Inner Mongolia, northeastern China, and the Hexi Corridor from the 1990s to the 2000s. Especially, remarkable increases were observed for Mongolia. Strong wind frequency (f(u>ut5%)) decreased or changed little over the period of study, and the 5th percentile of the threshold wind speed for dust outbreak (u(t5%)) decreased at many stations in Mongolia, eastern Inner Mongolia, and northeastern China. This suggests changes in erodibility factors increased fDO in these regions. There are stations where f(u>ut5%) increased and u(t5%) remained relatively constant in western Inner Mongolia and the Hexi Corridor. This suggests changes in the erosivity factor increased fDO at these locations. The change in erodibility is linked, in part, to the effect of dead leaves of grasses in spring, which are the residue of vegetation in summer from the previous year, which can cause an increase in the threshold wind speed. Citation: Kurosaki, Y., M. Shinoda, and M. Mikami (2011), What caused a recent increase in dust outbreaks over East Asia?, Geophys. Res. Lett., 38, L11702, doi:10.1029/2011GL047494.