This experiment was carried out to develop an ideal diluter for the preservation of liquic boar semen. In the second report, an excellent diluter was selected out of 10 diluters previously reported by other workers in and out of the country. The excellent diluent was set up as a control in this experiment. This experiment was systematically conducted to find more effective levels of dextrose, sodium citrate, potassium tartrate, egg yolk, E.D.T.A. and storage-temperature. Only sperm-rich part of the semen collected from 3 Landrace-boars was used. Semen eras diluted at the ratio of 1 to 3 and preserved at 0-5℃, 8-10℃ and 15℃, respectively. During the preservation-period, sperm motility and vitality were examined 6 times every 24 hours for 120 hours. The results were as follows: 1. The new excellent diluter was composed of dextrose … 3.5% sodium citrate … 0-0.29% potassium sodium tartrate … 0.02% egg yolk … 2-4% E.D.T.A.… 0.1-0.2% penicillin … 1000 IU/㎖ streptomycin … 0.1g/100㎖ Sperm motilities of the new diluter for 6 days were 73%, 70%, 60%, 60% and 53%, respectively. And those of the control were 72%, 65%, 55%, 17% and 0%. In sperm motility, significant difference was statistically recognized between the new diluter and the control(p$lt;0.01). 2. It was concluded that remarkable increase in sperm motility could be induced by using diluents added with E.D.T.A. at rate of 0.1 to 0.2%. 3. The optimum temperature for preservation was 8 to 15℃.