Aqueous dispersions of magnetic spherical polyelectrolyte brushes (MSPB) are prepared by mini-emulsion followed by photo-emulsion polymerization. Their viscosity increases dramatically upon increasing the intensity of an external magnetic field, showing the magnetoviscous effect. Unlike general magnetic nano-particles, the increase in viscosity of MSPB cannot be described by Shliomis's theory, probably due to the covering of a spherical polyelectrolyte brush layer. MSPB rheology is also tunable by pH, and the brushes can stay in atmospheric conditions for months without changes in particle size and size distribution, which should make them ideal candidates for a broad range of industrial applications. The future applications of our multifunctional magnetic responsive system are promising.