According to the Syrian standard 3411 & European standard EN 197-1, Portland pozzolana cements and Portland limestone cements can be produced by partial replacement of pozzolan or limestone up to 35%. Despite of the economical, ecological and technical benefits of adding natural pozzolan and limestone powder, they are often associated with shortcomings. The objective of the study is to investigate the effect of adding natural pozzolan, limestone powder or both on the mechanical strength development of the prepared cement mortars. In the study, sixteen types of binders (one OPC, six binary and nine ternary blended cements) with different replacement levels of natural pozzolan, limestone powder or both have been produced. The development of the compressive and flexural tensile strength of all mortar specimens has been investigated after 2,7,28 & 90 days curing, respectively. Test results revealed that there was a decrease in strength with increasing amounts of natural pozzolan. In addition, there was found an increase in the early age strength with adding limestone powder. The increase in compressive strength when adding both natural pozzolan and limestone powder has also been noted. Further, based on the results obtained, an empirical equation was derived to predict the mechanical strengths of binary & ternary blended cement mortars with curing times. The influence of adding natural pozzolan, limestone powder or both on some physical properties of binary and ternary blended cements have been reported, as well.