The invention relates to a method for manufacturing cellulose material, the method comprising introducing cellulose fibers as raw material pulp (1) to a system, adding an alkalizing agent into the system in order to absorb the alkalizing agent into the cellulose fibers (1), adding an anionic agent into the system in order to absorb said agent into the cellulose fibers (1), feeding the cellulose fibers (1) to a sieve plate press (6), performing a reaction between the cellulose fibers and the anionic agent at least partly in the sieve plate press (6) in order to produce anionized cellulose fibers having a degree of substitution between 0.05 and 0.35, wherein the reaction is performed at least partly at a consistency of at least 50%. In addition, the invention relates to a system for manufacturing cellulose material and to fibril cellulose produced from anionized cellulose fibers.