Abstract: The present invention relates to a method for providing a pretreated filler composition for use in paper and board manufacturing including the steps of: a) providing a filler comprising precipitated calcium carbonate, said filler being in the form of a slurry comprising no additives; b) providing at least one polymer selected from polyvinylamine or polyacrylic amide, said polymer having a charge density of an absolute value of at most 4 meq/g determined at pH 7; c) combining said at least one polymer of step b) with the filler of step a); d) providing a slurry of nanofibrillar cellulose; e) combining said nanofibrillar cellulose slurry with the formed combination of step c) and forming a pretreated filler composition comprising aggregates. Further it also relates to a pretreated filler composition prepared therefrom, and its use in stocks, paper and paper board.