Two types of microparticles, cationic silica particles (CSP) and cationic polymeric microparticles (CPMP), were used as flocculants and retention aids for solid suspensions in water and pulp, respectively The solid suspensions used in this study include both positively and negatively charged precipitated calcium carbonate (PCC) and negatively charged polystyrene latex. It was found that CPMP was not an effective retention aid for positively charged PCC suspension in pulp if it was used alone. However, the retention of PCC was improved when negatively charged PCC was used. The combination of cationic microparticle systems (CPMP and CSP) with either cationically or anionically charged water-soluble polyacrylamides could significantly improve the flocculation and retention. The possible mechanisms of flocculation of solid suspensions with different dual-flocculant systems were discussed.