PURPOSE: To prevent the aggregation of fine powdery silica and prepare a polyester containing a specific amount of the fine powdery silica having a specific particle diameter, by polymerizing a prepolymer having a specific viscosity in the solid phase.

CONSTITUTION: 0.01W5wt%, based on the weight of the formed polyester, fine powdery silica, prepared by the dry method, and having ≤0.1μ average primary particle diameter is dispersed preferably in ethylene glycol and added to a reaction tank. A polyester prepolymer having 0.2W0.4 intrinsic viscosity is used and polymerized in the solid phase within preferably 180W240°C temperature range under ≤0.1Torr reduced pressure or under nitrogen flow at ≤-60°C dew point to give the aimed polyester containing the silica.