To provide a method of manufacturing a fine fibrous cellulose which has a long fiber length and is high in the yield of the fine fibrous cellulose in a fibrillation step.

A method of manufacturing a fine fibrous cellulose includes: a preparation step of pulp including mechanical pulp; a chemical treatment step of applying chemical treatment to the pulp including the mechanical pulp by at least one of followings (a) to (d); and a fibrillation step of fibrillating the pulp after the chemical treatment. (a) An ozone treatment, (b) a treatment with acid anhydride of a compound having carboxy group, (c) a treatment with a compound having phosphoric acid group, and (d) a treatment with an enzyme.