This experiment was performed to clarify the effect of lipid decreasing factor included in the seminal plasma of bull semen on the content of various phospholipids and neutral lipids in boar spermatozoa. Total phospholipids and total neutral lipids extracted from boar spermatozoa after incubation and freezing with the solution of bull plasma protein were fractionated quantitatively on the column of Dowex-I and silica gel, respectively. The results obtained in this experiment were as follows: 1. Total phospholipids extracted from boar spermatozoa were fractionated into 12 fractions and the content of each fraction in boar spermatozoa were decreased significantly(P$lt;0.02) by the action of lipid decreasing factor included in bull plasma protein. Decreasing rates were ranged from 38.24 to 47.36%. 2. The content of neutral lipids such as cholesterol-ester, free cholesterol, mono-, di-, and tri-glyceride in boar spermatozoa were also decreased significantly (P$gt;0.01) by the action of lipid decreasing factor included in bull plasma protein. Decreasing rates of cholesterol-ester, free cholesterol, mono-, di-, and tri-glyceride were 28.62, 30.85, 59.65, 55.49, and 54.32, respectively. 3. Possibility that lipid decreasing factor included in bull seminal plasma is not a lipid hydrolyzing enzyme but a specific factor which extracts all sort of lipids from spermatozoa was increased by the results of present experiment.