Experiments of rapid freezing of boar semen using the semen container made of aluminum pack in the vapor of liquid nitrogen were carried out. Semen was collected from 4 Middle Yorkshires, 1 Berkshire and 2 Landraces. The semen was stored at -196°C in liquid nitrogen and motility of spermatozoa before freezing and after thawing was examined. Fertility of frozen boar semen was also tested. The results obtained are as follows:
　1) Survival of spermatozoa after a rapid freezing using aluminum packaging semen container with the vapor of liquid nitrogen was 25%-60%; with an average of 57.7 %. Rapid freezing was superior to slow freezing.
　2) Within a range of 0.5-20 hours, the semen equilibrated for 3-6 hours gave high percentage of motile spermatozoa.
　3) Good survival and high percentage (40-60%) of motile spermatozoa was shown after storage in liquid nitrogen up to 900 days.
　4) The semen stored for 4 to 532 days at-196°C was inseminated to 8 sows and 12 gilts. The results were 14 conceived and 96 piglings were farrowed out of 12 sows and gilts (2 aborted). The longest record of storage with satisfactory conception and farrowing in sows and gilts was 510 days and a record-setting gilt has farrowed a litter of 10 piglings.