The paper presents some aspects of settling and filtration of very fine alumina trihydrate particles in Na-aluminate-caustic liquor. The work carried out on laboratory scale shows that flocculation can be effectively used for improving the settling behaviour. The effect of additive, solids concentration, pressure, etc., on filtration characteristics of trihydrate slurry is also investigated. Application of laboratory scale tests for design and scale up of filtration operation are studied. A concept of an average specific cake resistance term developed from pressure and concentration parameters is proposed to be considered for filtration rate calculations.