Flocculation of paramagnetic particles under the influence of a strong magnetic field is reported in this article, Experimental information is obtained from fluctuation and intensity measurements of light passing through a particle suspension introduced in a uniform magnetic field, The magnetic field of strengths up to 6 T is generated by a cryogenic magnet operating at liquid helium temperatures. The phenomenon is analyzed by a Brownian flocculation model in which hydrodynamic, van der Waals, double-layer, and magnetic forces are incorporated for the estimation of the particle-flocculation rate. A population balance is employed in conjunction with the flocculation model to predict the evolution of the particle state with time, The effects of such important parameters as strength of the magnetic field, magnetic susceptibility of the particles, particle size, and zeta potential are investigated. Results show that particle size and magnetic susceptibility each play an important role in the selective flocculation of particles of different properties.