This article gives a discussion of the accelerating effects of tertiary amines in hardening unsaturated polyester. For this purpose, by using 2-methyl-1,3-propandiol, terephthalic acid, and maleic anhydride, an unsaturated polyester polymer was synthesized in a pilot reactor with a heater control. Stannous oxalate was used as an esterification catalyst. The polymer was dissolved in styrene containing a small part of hydroquinone. Cobalt octoate in toluene (1% m/m of Co) or and tertiary amines such as (DMA), (DMPT), (DHEPT), (PTDEA), and (TMEDA) were evaluated as curing reaction promotors or copromotors for the unsaturated polyester resin by using 1% methyl ethyl ketone peroxide (MEKp, Butanox M60). The increase of cobalt concentration for curing 100 g of unsaturated polyester resin by using 1 mL MEKp reduced gel time and curing time but increased peak exotherm temperature. Tertiary amine promotors, at a constant 1% MEKp and 0.5% cobalt solution catalyst system, were evaluated for efficiency as indicated by decreased gel and cure times: DMPA > DMA much greater than DHEPT > PTDEA greater than or equal to TMEDA.