Abstract: Objective: Short tandem repeats （STRs) sequences 4A, 9A and 9B were used to detect gene duplication of Charcot Marie Tooth disease type 1A（CMT1A). Methods: Polymorphism and heterozygosity of STR 4A, 9A and 9B were analyzed in 100 normal controls using polymerase chain reaction and Single strand conformational polymophisms （PCR SSCP). Then STR 4A, 9A and 9B were used to detect gene duplication in 30 unrelated CMT1 patients. Results: The polymorphism of the 3 markers is 8, 12 and 11 respectively. The heterozygosity of them is 0.75, 0.84 and 0.81 respectively. 60%（18/30) of CMT1 patients were detected gene duplication using 3 markers. The rate is higher than that（52 9%) which was detected by the primary markers in our laboratory. Conclusion: Both polymorphism and heterozygosity of STR 4A, 9A and 9B are high in normal controls and in CMT1 patients. Especially 9A and 9B have the highest observed hetero zygosity reported to date for CMT1A markers. They are the ideal markers to detect CMT1A gene duplication clinically.