Knowledge of the G6PD genotype and its associated enzyme activity is significant for population genetics, diagnosis of disease, and management of patients. We tested 2,872 unrelated subjects from a Hakka population in China for G6PD activity by the WHO standard method and for genotype by DHPLC and DNA sequencing. Among female heterozygotes, 78.5% had relatively normal enzyme activity. The phenotype frequency of G6PD deficiency is 0.028, and the causal allele frequency is 0.060 in females. The accuracy, sensitivity, and specificity of DHPLC are more than 98% for detecting G6PD-deficient hemizygotes, heterozygotes, and homozygotes. Measuring enzyme activity alone is not sufficient for the diagnosis of heterozygotes. A combination of enzyme activity and DNA analysis should be used.