An experimental study on the single-feed semibatch precipitation of barium sulphate was conducted. The effect on the crystal size distribution of a number of process variables including the volume ratio of reacting solutions, mean initial reactant concentration, stoichiometric ratio of reactants, impeller speed and feed location was investigated. Additional experiments were carried out to assess the effect of backmixing in the feed pipe and mesomixing near the feeding point on the crystallization process. The experimental results can be interpreted on the basis of the mixing scales existing in the precipitation tank and their impact on the relative magnitude of the rates of nucleation (heterogeneous or homogeneous) and crystal growth.