In this experiment effects of straw-size, glycerol equilibration time, thawing temperature, centrifugation of semen, kinds of diluent and addition of ethylene diaminetetraacetic acid 2 Na (E.D.T.A), egg yolk, skim milk and sugar on motility and livability of frozen boar semen were studied. The results obtained from this studies were as follows: 1. The highest post-thawing livability was obtained from the diluted semen exposed to glycerol for 4 hours and from the semen thawed at 40℃ rather than at 10℃. 2. The boar semen in 0.5㎖ straw showed higher post-thawing livability than the semen in 1㎖ straw. 3. 0.2 percent of E.D.T.A and 10 to 20% of egg yolk in the diluent showed higher post-thawing livability between 10 and 20% of egg yolk in diluent. 4. The basic egg yolk tris buffer was modified in this experiment as follows: Trisarminomethane 3.078g, citric acid 1.780g, glucose 0.3g, fructose 0.3g, Glycine 0.48g, catalase 0.02g, E.D.T.A. (Na₂) 0.2g and egg yolk 20㎖ were adjusted to 100㎖ distilled water. One mg of streptomycin arid 1,000 I.U. of penicillin per ㎖ were added to this diluent. 5. The boar semen in skim milk diluent without glycine showed higher post-thawing livability than the semen in skim milk with glycine. 6. The highest post-thawing livability was obtained from the semen diluted with diluent containing 5 to 7% of skim milk and 6% of glucose. 7. The semen diluted with skim milk extender containing 3% of glucose and fructose respectively showed highest post-thawing livability. 8. The basic skim milk diluent was modified in this experiment as follows: skim milk 5g, glucose 3g, and fructose 3g were adjusted to 100㎖ distilled water.