Pd nanoparticles (NPs) supported by micelles formed with poly(2-(dimethylamino)ethyl methacrylate)-b-poly(lauryl methacrylate) (Pd/PDMAEMA-b-PLMA) were prepared and employed as catalyst in the Suzuki-Miyaura cross-coupling reaction of aryl bromides with arylboronic acids in water. Most reactions proceeded with high efficiency at room temperature with only 0.05 mol% Pd loading in the absence of ligands, which afforded the desired functionalized biaryls in 73–98 % yields after 24 h. After reaction, Pd/PDMAEMA-b-PLMA retained in the aqueous phase was easily separated from the insoluble biaryl product and could be further reused two times without significant loss in catalytic efficiency. Characterization of the catalyst disclosed that sub-2 nm Pd NPs were embedded in the hydrophilic corona of polymeric micelles that served as nanoreactors in water.