The "gray zone" of borderline hemoglobin A2 (Hb A2) may be present in a large section of the population, especially in countries where thalassemia is common. However, very little is currently known of the molecular basis of borderline Hb A2 in Chinese individuals.In this study, we performed a comprehensive analysis of the globin genotypes and KLF1 gene mutations associated with borderline Hb A2 in 165 Chinese subjects.Fifteen (9.1%) were positive for a molecular defect in the α-,β-globin genes, of whom, α-thalassemia mutations and α-globin gene triplication were found in eleven cases, accounting for about 73.3% of these globin gene defects. Twenty (12.1%) were positive for a molecular defect in the KLF1 gene. Eight different mutations were identified, six of which are here reported for the first time. The most common is the G176AfsX179 mutation, accounting for 50% of the total.The molecular characterization of borderline Hb A2 in Chinese individuals is significantly different than in Italian population. Our data is conductive to provision of genetic counseling for Chinese individuals with borderline Hb A2.