Reverse atom transfer radical polymerization (RATRP) was used to synthesize poly(dimethyl itaconate) (PDMI) using an AIBME/CuBr₂/dNbpy system. The number average molecular weight (M_n) of PDMI was as high as M_n = 15 000 g mol⁻¹, the monomer conversion rate reached up to 70%, and the dispersity remained low (Đ = 1.06–1.38). The first-order kinetics of PDMI are discussed in detail. The AIBME initiator had a higher initiation efficiency than the AIBN initiator. As the ratio of initiator (AIBME) to catalyst (CuBr₂) decreased, the M_n and Đ of PDMI decreased. At 60 °C and 80 °C, the M_n of PDMI was much higher than the theoretical number average (M_n,th), and the Đ of PDMI broadened with the conversion rate. At 100 °C, the Đ of PDMI remained low, and the M_n of PDMI was closer to the M_n,th. As the ratio of monomer (DMI) to initiator (AIBME) increased, the M_n of PDMI changed little over time. These phenomena could be explained by the influence of the initiator and catalyst on polymerization kinetics.