IN THIS work the effect of prepared melamine formaldehyde sulfanilate (MFS) and cyclohexanone formaldehyde sulfonate (CFS) on the physico-chemical properties of the hardened OPC pastes was investigated. The investigation included the determination of the chemically combined water and free lime contents as well as the compressive strength of the hardened admixed cement pastes at different time intervals. Besides, the rheological behavior of the fresh cement pastes was studied. The phase composition of the formed hydration products was identified by using X-ray diffraction analysis. The results showed that as the dosage of admixtures increases, the water of consistency decreases; this leads to a decrease in the initial porosity of the cement pastes, and consequently the compressive strength values increase. Also as the admixture dosage increases, the extent of adsoption on the surface of cement particles increases. This leads to an increase of the negative charge on the cement particles with strong repulsion between them and a consequent enhancement of the rheological properties of cement pastes. The results of X-ray diffraction analysis indicated that the main hydration products formed are the nearly amorphous calcium silicate hydrates (mainly as CSH-I and CSH-II), calcium sulphoaluminate hydrates (ettrringite and monosulphate hydrates) and portlandite (CH).