The phosphorus-containing polycarbonate polyol disclosed herein has a structural unit (I) represented by a formula: —OCOO— and a structural unit (II) represented by a residue A, wherein A denotes a n-valent residue in which n of alcoholic hydroxyl groups are removed from a phosphorus compound having at least n of alcoholic hydroxyl groups, in which n is an integer of 2 or larger, and wherein a terminal group of the polyol is a alcoholic hydroxyl group. The novel phosphorus-containing polycarbonate polyol, as a reactive flame-retardant agent, can provide flame-retardant properties easily to polyurethane or the like.