This experiment was Carried out to develop a diluent fer the freezing storage cf boar semen. In this experiment, an excellent diluent was selected out of 5 diluters reported previously by other workers. The excellent diluent was set up(as a control in this experiment, and the most effective levels of Various chemical components, egg yolk and glycerol and dilutionrate were determined. Only sperm-rich portion of the semen collected from a Large-White freed boar was used. In each treatments, sperm motility and Viability of frozen Semen were estimated after thawing in water of 40℃ for 2 min. The results obtained were as follows: 1. The best result was obtained f tom tris-yolk-glucose diluent. 2. optimum concentrom of tris, citric acid and gluccse were 6,056, 3.4 and 3.0g per 100㎖, respectively, and these of clarified and egg zalk atere 2.08 and 25㎖ per 100㎖ of diluent. 3. optimum dilution roate was clarified to be three tincos. 4. The composotion of new diluent (basic diluent A) recommended cues as follows: Tris (hydroxy methyl) amino methane … 6,056g citric acid …3.4g glucose (dextrose) … 3.0g Ethylene Diamine tetraacetic Acid (4Na)… 0.3g Penicillin … 1000IU/㎖ streptomycin … 0.2g distilled water … 170㎖