The purpose of this paper was to study the sex differences in infant mortality and mortality before the age of 5 in China, and the differences between urban and rural areas on the one hand and urban areas of mainland China and Hong Kong on the other. Published data from the 1982 and 1990 national censuses, the mortality survey of 1976, and UN's publications were used to calculate sex differences and sex ratios of mortality. Infant mortality of both sexes decreased notably from the 1970's onwards, the sex ratios of mortality being 1.15 in 1973–75, 1.06 in 1981 and 0.86 in 1990. A remarkable decline of mortality before the age of 5 was also seen in both sexes, but the sex ratios of mortality were not greatly altered, remaining less than 1 from the 1970's on. In rural areas female infants and young children had a higher mortality compared with males than in urban areas. In Hong Kong, the sex differences of infant and early child mortality were much smaller than in urban areas of mainland China.