Influence of the degree of particle dispersion on flow properties and the classification effect in the roll hip were investigated for roll milling of highly viscous suspensions. Seventeen kinds of commercial powders were dispersed into a linseed oil varnish with a three-roll mill, and the changes of the flow properties were measured. The rheological differences of these suspensions were classified into four groups and were discussed qualitatively in the light of the Casson's equation of viscosity. -- AATA