A few technical methods for care and breeding of mice (dd-strain uniform-strain) were investigated. In an experiment with special reference to mice's body weights, mice of different weight were weighed and some mice were separated from the others. When the mice separated were moreover screened by the same way after two days, the uniform mice whose weights had shown little change were gotten. The condition of breeding and growth of mice was observed for a year. And two calculations of the weight-keep rate (the ratio of number of the mice with uniform weight to total number including the young mice) and the supply rate (the ratio of number of the mice which can be supplied with uniform weight to number of mice [female] in a cage) were contrived. As the capacity to breed mice and number of the mice which can be supplied with uniform weight may be guessed by obtaining these rates, a stable breeding and supply program will be easiy planned. In the present experiment, the weight-keep rate was about 0.7∼0.8 and the supply rate was about 2.0∼2.5 (only female).