Using survey data from China, this article examines the effects of income gaps on migration decisions and the sources of these gaps. The econometric results support the hypothesis that income gaps significantly influence migration decisions. When income gap reaches a certain level, the reaction of the migration probability to income gap is weaker for men than for women. The relative income of women is less sensitive to an increase in rural income but more sensitive to a decrease in urban income than that of men. Moreover, we find that the urban to rural income gap is larger for women than for men, which suggests that women receive larger monetary return from migration than men do. In decomposing income gaps, we find that the gap for men is largely determined by differences in the attributes of migrants and nonmigrants, whereas for women, the gap is mainly determined by differences in returns to attributes.