In this study, the authors use micro-data for nationalities to study differences in fertility behavior in China. Working with a sample of cases from the 1990 Census in Xinjiang Uighur Autonomous Region, two issues previously only studied at the all-China level were considered: (1) the factors which determine whether couples with at least one surviving child have an additional child, and (2) sex ratios at birth. Differences by nationality are potentially informative, because the one-child family policy has generally not been applied to minority nationalities, although higher specific targets have been established. Moreover, ethnic differences in fertility have been masked in previous analyses that relied either on data for all of China or for provinces, so that we know very little about the extent of ethnic differences in fertility in China. The study compares aspects of the fertility behavior of the four largest nationalities in Xinjiang Uighur Autonomous Region: Uighurs, Kazakhs, Hui, and Han. The study reveals very different patterns of sex-selective fertility behavior by the different nationalities, both in the decision to have an additional child and in the sex of newborn children. Evidence which has not previously been noted in other studies shows a preference for girls under certain conditions.