Iron(II)-catalyzed suspension living radical polymerizations of acrylates and styrene have been achieved for the first time in water. In the presence of a large amount of water (water/organic = 1/1 v/v), a half-metallocene type iron complex [Fe(Cp)I(CO)(2)] induced a smooth polymerization of n-butyl acrylate in conjunction with (CH3)(2)C(CO2Et)I as an initiator to give polymers of narrow molecular weight distributions (MWDs) (M-W/M-n = 1.2-1.3) and controlled number-average molecular weights, in direct proportion to monomer conversion. Reaching 90% conversion in 4 h, the polymerizations proceeded much faster than in toluene without water. Similarly, methyl acrylate, tert-butyl acrylate, and styrene were polymerized with the same initiating system under aqueous suspension conditions to afford living polymers of controlled molecular weights and narrow MWDs (M-W/M-n = 1.2-1.3). The suspension systems can be applied to the controlled synthesis of block and random copolymers of acrylates and styrene.