This experiment was carried out to clarify the effect of lipid decreasing factor included in bull seminal plasma on the physiologic activity of spermatozoa. The changes in visibility and metabolic activity of boar spermatozoa treated with lipid decreasing factor after removal of seminal plasma were examined with or without metabolic substrate during storage at various temperatures. The results obtained were as follows; 1. Viability of boar spermatozoa was improved significantly (p$lt;0.01) by the action of lipid decreasing factor extracted from bull seminal plasma during storage at 37,15 and 4℃ for certain period with metabolic substrate. 2. Oxygen uptake of boar spermatozoa was facilitated significantly (p$lt;0.01) by the action of lipid decreasing factor during incubation at 37℃ for 180 minutes under aerobic condition with metabolic substrate. 3. Glucose consumption of boar spermatozoa was also promoted significantly (p$lt;0.01) by the action of lipid decreasing factor during incubation at 37℃ for 180 minutes. 4. It could be concluded from the above results that lipid decreasing factor included in bull seminal plasma facilitated the viability of boar spermoatzoa by the means of improvements in respiration and glycolysis of boar spermatozoa under aerobic condition with metabolic substrate.