To obtain a high-purity lubricant suitable for producing a magnetic recording medium excellent in traveling properties, wear resistance and durability, by esterifying a terminal carboxyl perfluoropolyether synthetic substance, extracting the esterified compound with a solvent and hydrolyzing the extracted substance.

A terminal carboxyl-containing perfluoropolyether synthetic substance is esterified with an alcohol containing a relatively long hydrocarbon chain (e.g. 1-octadecanol), etc., and the prepared reaction product is extracted with a solvent such as hexane or an ether to separate and remove impurities and the extracted esterified compound is hydrolyzed with a solution of sodium hydroxide or potassium hydroxide to give the objective lubricant.