PURPOSE: To prepare the titled compound useful as an antistatic agent and emulsifying agent economically in high yield, by reacting a triglyceride of an inexpensive natural fat or oil, etc. as a raw material with glycerol and boric acid under specific conditions.

CONSTITUTION: 3 moles boric acid is reacted with 1W2 moles at least one of triglyceride of a long-chain fatty acid, e.g. preferably an 8W22C fatty acid and natural animal or vegetable fat or oil, and 4W5 moles glycerol in a neutral W acidic state at 240W280°C to give the aimed boric acid ester of glycerol ester of the fatty acid which is a mixture of compounds expressed by formula I [X, Y and Z are OH or RCOO- (R is 7W23C alkyl)] with formula II.