Effects of admixture type and dosage have been investigated in the scope of this study. The influence of incorporation of chemical admixtures at different dosages on the development of pore structure of cement mortars has also been investigated. A delay on the development rate of strength by incorporation of chemical admixtures at early ages has been determined. The highest strength values were obtained for the cement mortars prepared by naphthalene sulphonate based chemical admixture. The strength values of specimens prepared with overdosage were lower than those of control specimens. Therefore, setting time and flow values were investigated related to admixture dosage and type. Increase in dosage of admixtures results in an increase of setting time and flow values. The pore structure development was given by time and dosage. Maximum pore area ratio values are determined for cement mortars prepared with overdosage. Pore area ratio values decrease by time, as compressive strength values increase.