Four sizes (0.095, 0.53, 1.0 and 2.01μm) of polystyrene latex particles were used to prepare monodis-persed suspensions at three different ionic strengths (10?3, 10?2.5 and 10?2M KCl). Filtration experiments were conductedusing those suspensions in a filter column with glass beads as porous medium. The filter bed depth and the filtrationvelocity were kept at 5cm and 1m/h, respectively. When suspensions with equal mass concentrations (0.2mg/L) orequal surface area concentrations (0.12cm2/mL) were filtered through the system, the largest particles exhibited higherinitial single collector efficiency, η. The difference between the η of largest particles and the smaller particles was prominent for suspensions with equal surface area concentrations at higher ionic strengths. The collision efficiency, α ofthose particles exhibits higher values at higher ionic strengths. Both at equal mass concentration and equal surface areaconcentration, α is only slightly dependent on particle sizes when compared to its dependence on ionic strength. Further,it was found that the specific surface coverage was similar for 0.095μm, 0.53μm and 1.0μm particles during thetransient stage of filtration at any ionic strength when the surface area concentrations of those suspension were equal.