The grandfather-father-son relationship of the first three lords of the Date clan in Japan was ascertained by HLA-DNA sequencing analysis. From their hairs and dried lung tissue found in ca. 300-year-old remains, DNA was extracted with usual phenol-chloroform method followed by purification with cetyltrimethylammonium bromide (CTAB). Two HLA class II genes, HLA-DQA1 and -DPB1, were amplified by seminested, or dual/triple PCR. The PCR products were cloned and analyzed by automated sequencing. Since the three lords shared a haplotype of DQA1*0301-DPB1*0402, we concluded that there is no inconsistency in their lineage. This is the first case of biological evidence for a historical Samurai family relationship in the 17-18th centuries.