The number of people who moved from Seoul to other regions was 421,887 last month, which is more than 22,367 who moved to Seoul (398,720), according to the data compiled by Statistics Korea.
Last year, the figure was the lowest in 43 years due largely to a rise in housing prices and rapid aging.
Housing prices in Seoul rose sharply last year despite a series of measures to rein in surging prices, including tightened home mortgages.