The results are presented on the synthesis of new modifiers for unsaturated polyester resins, obtained by reacting ethylene oxide or propylene oxide with phenylene-1,2-diamine. The effect of the modifiers and cobalt accelerator on the reactivity of resins was also studied. When used in the amount of up to 1.50 wt.-%, the amines substantially (several times) reduced the gelation time of modified unsaturated polyesters. The reactivity of resins, however, improved on the expense of their stability.