Abstract: The hairless mutant mouse was found in KM closed colony. The “hairless” gene was retained by backcrossing and brother X sister mating system. The inbreeding had progressed to the 18th generation since February 1995. The average generation interval was 71.5 days (55-116 days). The result of coat color test crossing of the F18 with DBA/2 showed that the color genes in F18 were homogenous. The hairless mice start to shed at the age of 4 weeks and lose almost all hairs at the age of 5 weeks. The sparse and short hairs gradually appear after the age of 6 weeks. Clean hairle'ss mice have been derived through caesarean section.