Cationic polyacrylamides of very high molecular weight and with different charge densities and degrees of branching have been investigated as retention aids for papermaking. The effects of polymer charge density and polymer branching on drainage and retention of a suspension containing fibers and precipitated calcium carbonate have been correlated with floes properties. Additionally, the effects of flocculant dosage and contact time with the furnish were investigated. Results show that polymers of medium charge density are more adequate to be used as retention aids since lower drainage time and higher filler retention are obtained at short contact time and low flocculant dosage. The branched polymers exhibited better performance than the linear polymers: drainage performance is significantly improved because highly branched polymers produce small floes with a more open structure.