A reinforcing fiber structure for a propeller blade made of composite material is woven as a single piece to have an airfoil, a spar portion, and an enlarged portion. The fiber structure includes a zone of non-interlinking extending between the front and rear edges of the airfoil, and extending between an intermediate zone and the bottom edge of said airfoil. The spar portion extends inside the airfoil in the zone of non-interlinking, the spar portion extending outside the airfoil through the bottom edge of said airfoil. The enlarged portion extends from the spar portion outside the airfoil. The airfoil includes skins that are not interlinked with each other in the zone of non-interlinking and that surround the spar portion. The skins define two housings present inside the airfoil on respective sides of the spar portion and opening out through the bottom edge of the airfoil.