A process of making filled paper comprising the steps of providing a thick stock cellulosic suspension that contains mechanical pulp and filler, diluting the thick stock suspension to form a thin stock suspension, in which the filler is present in the thin stock suspension in an amount of at least 10% by weight based on dry weight of thin stock suspension, flocculating the thick stock suspension and/or the thin stock using a polymeric retention/drainage system, draining the thin stock suspension on a screen to form a sheet and then drying the sheet, in which the polymeric retention/drainage system comprises, i) a water-soluble branched anionic polymer and ii)a water-soluble cationic or amphoteric polymer. The process is particularly suitable for making filled mechanical grade paper, such as SC grade paper. The process enables the separation of retention and drainage parameters, especially useful for fast draining paper machines, such as Gapformers.