Abstract: The process according to the invention consists in that the freshly collected ram semen is first diluted at between 25.degree. and 32.degree.C and notably at 30.degree.C, in a diluent without glycerol containing lactose and egg yolk, and in then diluting, at between 3.degree. and 5.degree.C and notably at 4.degree.C, the mixture previously obtained in a diluent containing glycerol, said diluent essentially comprising powdered milk and sodium citrate, in conditioning in straws the so diluted semen and in freezing it in liquid nitrogen at about -75.degree.C. The invention also relates to the diluent used in the above process.The process is useful for preserving ram semen by freezing for subsequent artificial insemination of ewes.