Calcium silicate hydrate (C-S-H) is the most important binding phase of cement paste and can determine the mechanical properties of cementitious material. The multi-scale nature of C-S-H gel brings about challenges in interpreting the mechanical properties of C-S-H. C-S-H models at the nano scales are commonly formulated by the aggregation of colloids that consist of layered molecular structures. In this study, the mechanical properties of C-S-H were investigated at the molecular level (∼5 nm). Uniaxial tension testing in the x, y, z directions was applied to the layered structure of C-S-H. The structural difference in the layer leads to heterogeneous mechanical properties in three directions. Particularly in the z direction, the C-S-H layer connected by H-bonds and Ca, has the weakest tensile strength. Resulting from the investigation, it can be concluded that the simulation can provide molecular insights into the linkage between molecular and larger scale structures. © 2014 Elsevier B.V. All rights reserved.