The atom transfer radical polymerization (ATRP) of n-butyl acrylate (nBA) using initiators for continuous activator regeneration (ICAR) was successfully carried out in ionic liquid in the presence of a catalyst system of FeCl3·6H2O/succinic acid using 2-bromoisobutyrate as the initiator and 2,2′-azobisisobutyronitrile as the reducing agent. The ICAR ATRP of nBA was proved a ‘living’/controlled polymerization such as a linear increase of molecular weights of polymers with monomer conversion and relatively narrow polydispersities (<1.25) when the conversion was beyond 30% and its kinetics in this system was investigated. The polymerization rate increased with temperature and the apparent activation energy was calculated to be 32.84 kJ mol−1. The chain extension experiment was carried out to confirm the controlled manner of the polymerization system. The resultant was characterized by nuclear magnetic resonance and gel permeation chromatography.