Way of synthesis of unsaturated polyester orthophthalic resin is presented. Properties of following materials are compared: of the synthesized resin before and after its hardening, of the polymer-concrete produced with its application, and of the polymer-concrete obtained with use of the orthophtalic resin modified with a terephthalalic one. The recycled polyethyleneterephthalate (PET) was applied to the synthesis of unsaturated terephthalic resin.