To provide a flexible polyurethane foam having improved sound absorbing properties in a low frequency region.A process for producing a flexible polyurethane foam which comprises foaming a starting material composition (E) comprising a high molecular weight polyoxyalkylene polyol (A), an organic polyisocyanate compound (B), a blowing agent (C) and a catalyst (D) in a closed mold, characterized in that at least a part of the high molecular weight polyoxyalkylene polyol (A) is a polyoxyalkylene polyol (p) having at least two hydroxyl groups on the average and having a molecular weight (Mc) per hydroxyl group of from 1,800 to 2,800 and a total unsaturation value (USV) of at most 0.08 meq/g, and that the air flowability of a flexible polyurethane foam obtained by foaming the starting material composition (E) in a thickness of 26 mm, is at most 0.085 m.sup.3/min.