Saitohin (STH) is thought to be involved in the pathogenesis of many neurodegenerative diseases. Recent reports were inconclusive in showing that the Q7R polymorphism in the STH gene is associated with late-onset Alzheimer's disease (LOAD). We examined the Q7R polymorphism in 500 subjects (LOAD: 280; controls: 220) from Guangdong, China, by the Restriction Fragment Length Polymorphism method. Only one QR heterozygous and no RR homozygous variants were found. Our results suggest that the frequency of the R allele in the Han population is lower than that in Caucasian and African populations. The Q7R polymorphism is unlikely to contribute significantly to Alzheimer's disease susceptibility of the Han population in south China and the variation of the Q7R polymorphism among different ethnic groups might account for the varied clinical manifestations of some STH-related diseases.