The process where the fine fraction of peat slurry is dewatered by a special type of microfilter, and the coarse fraction by a filter press, was tested in bench scale. The effect of particle class, initial DS content, DS load, flocculants and their dosage were studied. In general, fractionation nearly doubled the capacity in the compression phase, but the final DS content did not rise significantly. The differences in the capacities between the particle classes were small in compression but high in microfiltration. The final DS contents were nearly equal in each particle class for both dewatering methods. Fractionation was not useful until the particle class was 500μm or bigger in microfiltration.