To investigate the coincidental rate of double heterozygous state of beta-thalassemia and alpha-thalassemia 1 in Guangdong area.One handred and forty-two DNA samples with beta-thalassemia trait were amplified by polymerase chain reaction(PCR) to detect alpha-thalassemia 1 gene. The positive cases were further detected by mutant primer PCR or by reverse dot blot hybridization (ASO/RDB) to confirm their beta-thalassmia mutations.Thirteen cases (9.15%) were identified to combine with alpha-thalassemia 1 gene. The mutant loci of beta-globin gene in these cases were that 5 were in CD 41-42 (-TCTT), 3 in IVS-2-654(C-->T), 2 in CD 17 (A-->T) and 3 in CD 71-72 (+A), CD 43(G-->T) and -28 (A-->G), respectively.The occurrence of this dual heterozygotes among beta-thalassemia trait is relatively frequent and it should be paid much attention to in genetic counselling and prenatal diagnosis of thalassemia in this area.