The article studies the possible factors that determine the popularity of rental housing units for expatriates in Seoul by employing the Poisson regression model. Previous literatures on the issue state that transaction frequency of housings is generally affected by market conditions, property conditions and other factors influencing buyer and seller decisions. Rental housing markets for expatriates working at foreign firms in Seoul are also presumed to be influenced by these attributes plus tenant characteristics. Using lease transaction data for the period of March 1984 through April 2013, the analysis finds out that as housing is getting smaller or its rent is getting lower, the transaction frequencies are increased. A similar results come out as did in the Previous Literatures of U.S. and H.K. The outcomes of the analysis indicate substantial variation in the incidence and the frequency of transaction across research areas and type of industry.