Method for producing fibrous cellulose， and fibrous cellulose

It is an object of the present invention to provide a method for producing ultrafine fibrous cellulose， which is capable of efficiently obtaining ultrafine fibrous cellulose having phosphoric acid groups with a high yield. The present invention relates to a method for producing fibrous cellulose having a fiber width of 1000 nm or less， comprising: a (A) of introducing phosphoric acid groups into cellulose fibers to form crosslinked structures via the phosphoric acid groups， thereby obtaining crosslinked phosphorylated cellulose fibers， a (B) of breaking some or all of the crosslinked structures to obtain crosslink-broken phosphorylated cellulose fibers， and a (C) of performing a mechanical treatment on the crosslink-broken phosphorylated cellulose fibers to obtain fibrous cellulose having a fiber width of 1000 nm or less， wherein， in the (A)， crosslinked structures in an amount of 0.05 mmol/g or more and 2.0 mmol/g or less are formed， and the (B) is a step of performing the hydrolysis of the crosslinked structures in an aqueous solvent with pH 3 or more.