High-sulfonated melamine-formaldehyde (HSMF) resins were prepared with 1.0-2.0 of sulfite/melamine (S/M) molar ratio. The factors affecting the preparation and the properties of the resin were studied. Chemical analysis indicated that there are 0.98-1.96 sulfonate groups per unit of the polymeric chain. The viscosity of HSMF resins is lower than that of sulfonated melamine-formaldehyde (SMF) resins, and the HSMF resins are more effective superplasticizers at small dosages of admixture.