PURPOSE: To provide a catalyst compsn. which contains germanium dioxide, i.e., a catalyst for polycondensation of low polymers in polyester production, in a high concn.

CONSTITUTION: The catalyst compsn. comprising a glycol as the main component and germanium dioxide is produced in two steps: a step wherein the dioxide is dissolved in the glycol by stirring a mixture comprising the dioxide and the glycol in an ammonia gas atmosphere or by passing ammonia gas through the mixture; and a step wherein excess ammonia in the soln. is removed. The compsn. is produced at a low cost and, having a high concn. of the dioxide and a low concn. of impurities, exhibits a high catalytic effect and is useful for producing a high-quality polyester resin.