Inverted emulsion, i.e., water-in-oil (W/O) type emulsion, was prepared from styrene solution of unsaturated polyester obtained from Mg salt of mono(hydroxyethyl)phthalate, ethylene glycol (EG), maleic anhydride (MA), phthalic anhydride (PA), and propylene oxide (PO). The inverted emulsion was much more stable than that of blank polyester obtained from EG, MA, PA, and PO, and further than the usual inverted emulsion prepared by treating styrene solution of commercial unsaturated polyester with triethanolamine. By polymerization, the inverted emulsion was transformed to a white solid which was dry to the touch. The water-containing cured resin obtained showed considerably higher physical and other properties than those of commercial unsaturated polyester.