Mouse Pc-1 (Ms6-hm) is a hypervariable minisatellite locus that is unstable during intergenerational transmission. This hyper-instability of Pc-1 is useful for detecting germline mutation using a small number of experimental animals, although its molecular mechanism has not yet been elucidated. We examined the effect of severe combined immune deficiency (SCID) mutation on the spontaneous germline mutation at the Pc-1 locus using the CB17 mouse strain. Our results showed that the frequency of spontaneous germline mutation at Pc-1 in the offspring of wild-type parents was 9.7%. In F1 between SCID male and wild-type female, however, the frequency of germline mutation was drastically increased to 42.3%. When SCID female mice were mated with wild-type male, the frequency of germline mutation in F1 was slightly increased to 13.6%. These results suggest that DNA protein kinase catalytic subunit (DNA-PKcs), deficiency of which causes SCID mutation, plays an important role in the stable transmission of a genome containing hypervariable tandem repeats to progeny in male germ cells.