Atom transfer radical polymerization (ATRP) of vinyl monomers mediated by Schiff base containing ruthenium-alkylidene catalysts was examined. The ATRP activity of the corresponding cationic complexes was also investigated using a water/toluene mixture and toluene as solvent. Our results show that both the counterion of the cationic complexes and the solvent used for the polymerization exert a remarkable effect on the reactivity of these complexes and the control over polymerization. These cationic ruthenium - alkylidene complexes are the first in their kind to perform the controlled radical suspension polymerization of methyl acrylate, methyl methacrylate, and styrene in water with good to excellent yields.