This paper analyzes the income mobility trend and determinants of incomemobility in Korea using the KLIPS data. The main findings of this paper areas follows. Firstly, it turns out that income mobility has had a decreasingtrend during 1999-2008 period. Secondly, the ratio of the middle income classto whole households has decreased while the upper income class and the lowerincome class have increased. As a result polarization of income classes and thedemolition of the middle income classes has proceeded simultaneously.Thirdly, a decrease in income mobility in the long-run will make thedemolition of middle income class and polarization of income distribution.We examined determinants of income mobility of households in bothdirections considering demographic factors, economic factors, and policyfactors. As expected, all three factors have significant effects on incomemobility in Korea. We found that there exists a critical age before whichprobability of income mobility increases as age increases and vice versa afterthat. In terms of economic factors, the more is the number of family and theless is the initial income, the more probable is upward income mobility. Also,the job status such as a regular job and a white color affects income mobility.In terms of policy variables, we find whether the household head goes throughthe OJT(On the Job Training) and receives social insurance also affect theincome mobility.The policy implications of this paper are as follows. The government needsto subsidize the OJT program in the private sector. Some social welfareprograms should be revised not to discourage the work incentive of workers.