The invention relates to a process for manufacturing paper, in which a filler is pretreated and suspended to form an aqueous slurry, the aqueous slurry obtained is combined with an aqueous suspension containing cellulose fibres to form a stock, the stock obtained is treated at least with a cationic retention agent and the treated stock is filtered to form paper. Retention and optical properties are improved by the filler being pre-treated with inorganic colloidal particles having an average size less than 100 nm.