Because of persistent economic pressure On cost reduction, inorganic fillers such as precipitated calcium,carbonate (PCC) have become increasingly economically attractive in the papermaking,process. The increase of filler level in paper can be achieved by adding it to pulp prior to the headbox, either as individual filler particles or as preaggregates, while maintaining paper strength and minimizing their negative impact Consequently, the floc structure and strength of PCC aggregates was studied using flocculants and dry strength agents, using static light scattering/diffraction (SLS), real time fluorescent video imaging (RTFVI), image analysis, photometric dispersion analysis (PDA), and scanning electron microscopy (SEM). It was found that, PEO/cofactor induced PCC aggregates were weaker at high shear and far more irreversible than those induced by the partially hydrolyzed polyvinyl formamide de copolymerized with acrylic acid (PVFA/NaAA) or cationic starch. Flocs produced at low polymer dosages were smaller and weaker than those produced at higher dosages, The number of discrete PCC particles in aggregates was measured using real time fluorescent video imaging Combined with image analysis Finally, we speculate that when two scalenohedral crystal type PCC particles aggregate, there is a small effective surface area to bind them, mainly through classical bridging or charge neutralization flocculation. Moreover, additional polymer adsorption results in higher coverage of the external and internal surfaces and prevents further aggregation due to electrosteric repulsion.