Background Identification of pathogen DNA from archaeological human remains is a powerful tool in demonstrating that the infectious disease existed in the past. However, it is very difficult to detect trace amounts of DNA remnants attached to the human skeleton, especially from those buried in a humid atmosphere with a relatively high environmental temperature such as in Asia. Methodology/Principal Findings Here we demonstrate Mycobacterium leprae DNA from archaeological skeletal remains in Japan by polymerase chain reaction, DNA sequencing and single nucleotide polymorphism (SNP) analysis. In addition, we have established a highly sensitive method of detecting DNA using a combination of whole genome amplification and polymerase chain reaction, or WGA-PCR, which provides superior sensitivity and specificity in detecting DNA from trace amounts of skeletal materials. Conclusion/Significance We have detected M. leprae DNA in archaeological skeletal remains for the first time in the Far East. Its SNP genotype corresponded to type 1; the first detected case worldwide of ancient M. leprae DNA. We also developed a highly sensitive method to detect ancient DNA by utilizing whole genome amplification.