We report the cationic polyelectrolyte (CPAM)-SiO2 nanoparticle (NP) interactions in suspension and in a sheet form, when mixed with microfibrillated (MFC), using dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) techniques. The CPAM-SiO2 NP suspensions were prepared by adding NPs into CPAM drop wise and composites were prepared by adding CPAM-SiO2 suspension into MFC and through standard paper making procedure. DLS revealed that increase in CPAM dosage creates larger sized CPAM-NP aggregates because more NPs can be picked up by stretched CPAM chains. SAXS study revealed that CPAM-SiO2 NP assembly in the formed nanopaper fits well with a spherical core shell model (with SiO2 partially covered with CPAM) and sphere model (SiO2 alone) combined together. Understanding the interaction between polyelectrolyte-NP system through such scattering techniques enables us to engineer novel cellulose based composites for specific applications.