To provide a method for manufacturing partial acid CMC without elution and flowage of the partial acid CMC to its purification solvent that occurs when a powder raw material of a CMC salt is used.

This method comprises (a) a step of forming an alkali cellulose from a raw material pulp and then producing an aqueous solution of a CMC salt by etherification of the alkali cellulose, (b) a step of neutralizing the aqueous solution of the CMC salt to adjust pH to 8.0 or lower, (c) a step of adjusting a solid concentration of the CMC salt to 30-80 wt.% by removal of a part of a solvent from the aqueous solution of the CMC salt the pH of which is adjusted at the step (b), and (d) a step of adding 1.1-1.3 times theoretical molar amount of an acid required for a target degree of the acid etherification to the aqueous solution of the CMC salt the solid concentration of which is adjusted at the step (c) and stirring the solution, and then heating and stirring it at 60-110°C for 30-60 min.

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