The effect of mixing intensity (power input) on the precipitation/ crystallization of barium sulfate in a two-feedstream (sodium sulfate, barium chloride) continuous stirred-tank crystallizer with mixed product removal was investigated through experiments and companion mathematical models. Crystal growth rate and nucleation rate were very sensitive to mixing intensity, with growth rate increasing eightfold and nucleation rate decreasing 100-fold as power input per unit mass was increased from 0.001 to 0.73 m2/s3 (0 to 1,200 rpm stirrer speed). Experimental results at high feed concentration were accurately described by a model accounting for homogeneous nucleation and kinetic growth of particles as well as turbulent mass transfer to particles and turbulent micromixing of feedstreams. The principal mixing effect was due to particle mass transfer, not micromixing. Experiments at low feed concentration were more difficult to model because of a more complex nucleation mechanism and altered particle morphology.