To clarify the effects of supplementary cementitious materials (SCMs) on the mechanical properties of cement based materials, micro-structurally designed cement pastes, which were prepared by adding mono-sized SCMs into ultrafine Portland cement, were subjected to compressive strength tests. By changing the type, the addition and the size of SCMs in the micro-structurally designed cement pastes, effects of SCMs particles on the compressive strengths of cement pastes were quantitatively characterized, and then classified into inherent characteristic effect, particle size refinement effect, and hydration effect. Specifically, compressive strengths related to inherent characteristic effects of clinker, granulated blast furnace slag (GBFS), fly ash (FA) and quartz sand (QS) were 50.8 MPa, 44.6 MPa, 39.6 MPa, and 36.0 MPa, respectively. In contrast, compressive strength related to particle size refinement effect increased to 4.2 MPa when the D50 of SCMs decreased to 2.4 pm. Compressive strengths related to hydration effect of clinker, GBFS, and FA can be as high as 30.8 MPa, 22.5 MPa, and 9.1 MPa, respectively. Finally, an empirical model was established and validated to predict the compressive strength of cement paste with SCM5. The results will give a better understanding on rational utilization of SCMs or inert fillers to prepare cement-based materials with qualified mechanical properties and durability. (C) 2017 Elsevier B.V. All rights reserved.