Stable colloidal nanoparticles of well-controlled water-soluble poly(oligo(ethylene glycol) monomethyl ether methacrylate) (P(OEOMA)) homo- and copolymers were successfully synthesized by inverse miniemulsionatom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) at ambient temperature (30 degrees C). Oil-soluble sorbitan monooleate (Span 80) surfactant, ascorbic acid as a reducing agent, oxidatively stable CuBr2/tris[(2-pyridyl) methyl] amine (TPMA) catalyst complex, and [initiator](0)/[CuBr2/TPMA](0) = 1/0.5 were selected for the controlled AGET ATRP inverse miniemulsion. The effect of reaction parameters on control over AGET ATRP and colloidal stability were explored. It was found that the use of water-soluble poly(ethylene oxide)-based bromoisobutyrate macroinitiators (PEO-Br) with long chain EO units, up to 90% ascorbic acid of Cu(II) complex, and appropriate amount of water resulted in the formation of stable colloidal particles with less than 200 nm diameter and well-controlled P(OEOMA) with M-w/M-n < 1.3. The addition of a long chain poly(ethylene glycol) monomethyl ether (PEOH) as a costabilizer improved colloidal stability without interfering the polymerization. A water-soluble CuBr2/bipyridine catalyst complex was also suitable for AGET ATRP of OEOMA in inverse miniemulsion. Finally, colloidal particles of well-controlled block copolymers of OEOMA with different sizes of OEO side chains (degree of polymerization of EO = 5 and 9) were produced with relatively low M-w/M-n = 1.3 at 85% conversion.