The invention provides a process capable of easily producing a water-soluble salt of a naphthalenesulfonate formaldehyde condensate with a reduced amount of unreacted formaldehyde. When naphthalenesulfonic acid is subjected to condensation reaction with formaldehyde to produce a naphthalenesulfonate formaldehyde condensate, a sulfite is added to the reaction system after the conclusion of the condensation reaction. When a cement dispersant composition is obtained, the process includes a step of neutralizing the condensate.