A scale-up experiments of CaCO3 precipitation in 0.3, 1.0 and 5.0 dm(3) crystallizers were performed. For small input concentrations an influence of scale on product size and output concentration was observed. However, for large input concentration there-was practically no effect detected. Bimodality of Particle Size Distribution (PSD) was once more time confirmed. Influence of the stirrer power input on PSD is most visible in the smallest vessel. A size-dependent ag,aggregation-disruption model was used for extracting kinetic information. An experimental evidence was obtained that by the same stirrer power input (micromixing, level) macromixing plays a very important role, deciding for output PSD and concentration.