The effect of the crystalline bed selected parameters on filtration efficiency of the suspension is presented. The system of ferrous sulphate monohydrate crystals in the sulphuric acid solution has been studied. The strong relation between mean crystal size and filtration efficiency was observed. Quadruplication of the crystal size from 10 to 40 mum caused six-fold increase of filtration efficiency, i.e. from 11,1(.)10(-5) to 69,4(.)10(-5) m(3)/(m(2.)s), respectively. Simultaneously with crystal average size increase, the final bed humidity diminished from 50 to 38 mass percent as well as the sulphate concentration in the solution has been limited to the level of 0,5 mass percent. Several indications concerning the industrial crystallization conditions enabling the crystal size increase have been given.