Calcium-silicate-hydrate (C-S-H) gel is the only evolving porous material phase in cementitious composites and contributes the most to the engineering properties of concrete and other cementitious composites. Due to the difficulty in obtaining large size C-S-H gel from cementitious composites, the estimation of the poroelastic properties of C-S-H gel is difficult. This paper presents a novel approach to extract the poroelastic properties of C-S-H gel from the experimental data of the coupled nanoindentation and scanning electron microscope method. Through this study, the effective poroelastic coefficients were estimated by considering the shapes of C-S-H granule and calcium hydroxide included in C-S-H gel.