Both upward and downward cake filtration experiments are conducted under constant pressure conditions, using calcium carbonate slurry. The effects of particle sedimentation on filtration performance are examined. The filtration rate in upward filtration becomes much larger than that in downward filtration because of the effects of particle sedimentation A theoretical model has been developed to describe the effects of particle sedimentation on properties of both upward and downward cake filtration. The filtration rates in both upward and downward filtration are evaluated using both compression-permeability cell data and batch sedimentation test data, on the basis of modern filtration theory. In addition, a method is described to determine the value of the coefficient of constant pressure filtration from both upward and downward filtration experiments. This study reveals that sedimentation can have a profound effect upon filtration behavior in upward and downward cake filtration of a particulate suspension.