Fine cellulose fiber has a dispersion with a very high transparency and viscosity. A method is for producing the fine cellulose fiber. In the cellulose fiber, a part of hydroxy groups of cellulose fiber is substituted with a predetermined functional group to introduce an ester of phosphorus-oxo acid, and substituted with a carbamate group to introduce a carbamate. The method for producing fine cellulose fiber includes adding an additive (A) and an additive (B) including at least one of urea and a urea derivative to cellulose fiber, heating the mixture at 100 to 210° C., washing the mixture, and then fibrillating the mixture, the additive (B) being added in an amount of 0.01 to 100 mol based on 1 mol of the additive (A).