A fibrous cellulose has an average fiber width of 0.1 µm or more and has a part or all of hydroxyl groups replaced with carbamate groups, in which a replacement ratio with the carbamate group is 1.0 mmol/g or more, and a fine ratio is 30% or more. A fibrous cellulose composite resin contains a fibrous cellulose and a resin, and the above fibrous cellulose In manufacturing fibrous cellulose, a cellulose raw material and urea or the like are subjected to a heat treatment to replace a part or all of hydroxyl groups of the cellulose raw material with carbamate groups, defibration is performed within a range in which an average fiber width is 0.1 µm or more, the heat treatment is performed such that a replacement ratio with the carbamate group is 1.0 mmol/g or more, and the defibration is performed until a fine ratio reaches 30% or more.