Composite cements have several technical, environmental and economic advantages, so in this study, we discuss the properties of cement composed of two raw materials of granulated blast furnace slag from Isfahan Steel Company (GGBFS) and Rafsanjan mine pozzolan. These two mineral additives were mixed with Portland cement type 2 of the Sepahan Cement Company and limestone, which are the main components of this composite cement. To study the interaction of two main additives in the composite cement, several chemical and physical tests were performed on these materials based on the international standards. At first, their chemical properties, activity and physical properties of the samples were determined. Eight cement mixtures were then prepared from these materials and the physical and mechanical properties of the prepared cements were measured. According to the results of compressive strength during 1 to 90 days mortar and due to the fluidity and setting of the fresh mortar, the proposed composition (typical mix) including 20% slag powder, 10% pozzolan powder and 2.5% limestone powder was selected for additional studies. The cement paste of this mixture and the control cement, slag cement (30% slag) and pozzolanic (30% pozzolanic) were curing for 120 days. After the hardening step, the samples were prepared and the SEM, XRD, TGA characterizations were performed on them. The obtained results revealed that the composite cement containing slag and pozzolan have a positive effect on each other, along with proper resistance of the slag and pozzolan against the chemical attack. The slag improves the ultimate and long-term compressive strength of the composite cement, gives a better flow to the mortar, and possesses a less permeability, while pozzolan performs better in the initial strength, setting time, and grind ability. The microscopic studies and TGA test also revealed that the pozzolan additive reduces the amount of Portlandite composite cement paste (cement vulnerability to chemical attacks). The study of crystals by XRD indicated that the slag possesses few crystals, whereas in the XRD patterns, numerous pozzolanic crystals were observed, which reduce the compressive strength in the composite cement. The SEM images and EDAX elemental decomposition also displayed that the pozzolanic crystals in the composite cement did not react with water after 120 days without any residual change. The experimental results revealed that two used materials possess positive effects on the properties of composite cement and improve the capabilities of cement.