To provide a defoaming agent composition containing a polyoxyalkylene compound as a main defoaming component in order to improve the initial defoaming property, the persistence of the defoaming effect, and the stability of the defoaming effect when the defoaming property is varied, particularly, owing to temperature change of a liquid.

This defoaming agent composition contains the polyoxyalkylene compound (A) shown by the general formula: R1-X-(Y)-Z-R2 (wherein R1 and R2 are each a straight-chained or branched-chained 6-22C alkyl or alkenyl group independently; X and Z are each -CO- or -O- independently; Y is a polyoxyethylene-polyoxypropylene group and contains ≥50 mol% polyoxyethylene), an organosiloxane polymer (B), and hydrophobic silica (C).