Previous literature in the Korean stock market has shown that the momentum effect is not observed during pre-2000 period while it is observed during post-2000 period. Given that market illiquidity has substantially decreased during post-2000 period, we examine whether the level of market illiquidity affect the momentum profits. The central findings are summarized as follows. First, our full-sample analysis shows that market liquidity is positively associated with momentum profits, meaning that the observed momentum effect during post-2000 period is related to the decrease in market illiquidity. Second, during pre-2000 period, when the market illiquidity is very high, the illiquidity of past losers is extremely high compared to that of past winners. However, there is no significant difference in illiquidity between winners and losers during post-2000 period. Third, based on this result, we conjecture that the momentum effect is related to the different compensation for liquidity risk between past losers and winners, and test whether this is indeed the case. We find significant momentum profits over the whole period when we consider the compensation for the liquidity risk of past losers and winners. In addition, during pre-2000 period, the return on momentum strategy that controls the liquidity risk is substantially higher than the actually observed momentum profits. In sum, our study suggests that the difference in compensation for liquidity risk between past losers and winners is very important in understanding the momentum effect in the Korean stock market.