The Chinese household registration system (hukou), which divides the population into "agricultural" and "nonagricultural" sectors, may be the most important determinant of differential privileges in state socialist China, determining access to good jobs, education for one's children, housing, health care, and even the right to move to a city. Transforming one's hukou status from rural to urban is a central aspect of upward social mobility. Using data from a 1996 national probability sample, we show that education and membership in the Chinese Communist Party are the main determinants of such mobility.