Recently, the share of monthly-rent-variable-deposit(MRVD) contracts has been rising rapidly in Korean rental housing market. With the increasing share of MRVD, the prevailing practice of rent default by tenants in Korea is hindering from forming a stable MRVD market. The resulting social problem due to the practice is that a higher rent is required to overcome the risk in the Korean rental housing market. This paper investigates the determinants of rent default by the tenants. The survey results show that a significant number of tenants are depending on their parents or relatives to prepare the deposit for Chonsei or MRVD. Their probability of rent default is smaller than that of the tenants who borrow the deposit money from bank. Also, there are strong correlations between the probability of rent default and household income(more directly rent to income ratio. That is, as household income gets low(or rent to income ration gets high), rent default probability increases. These relationship is confirmed by the following regression analysis. In addition, the regression results show that age, number of family members, and stable job position reduce the rent default probability.