In this work, the reinforcing effects of Graphene Oxide Nanosheets dispersions (GOD) on high strength cement mortar are investigated, evaluating possible improvements in mechanical properties, fluidity, Sorptivity and water absorption resistance. Mortar with water/cement ratio of 0.5, GOD dosage varying from 0 to 0.20% by weight of cement and sand at a proportion of 3× weight of the cement were prepared, in addition to 10% and 20% replacement/no replacement with Silica Fume and Metakaolin respectively to improve the GO nanosheets dispersion. The GO used in the matrix forms aggregate due to presence of divalent Calcium ions. Hence to split the particles vigorous mixing was done. The results indicate that the addition of GOD accelerate the cement hydration reactions, increase the compressive strength and tensile strength of the mortar, reduce the pore volume and harden cement properties. However, the fluidity decreased with increasing GOD content. The optimal compressive strength was achieved with samples designed with GOD dosage of 0.05% with replacement, for which the corresponding increases were 72.41%, 84.61% and 90.90%, after 3,7 and 28 days respectively, compared with samples without GOD and replacement. The tensile strength of the cement mortar increased with GOD content to 132%, 178.6% and 181.2% for 3, 7 and 28 days respectively with replacement and GOD dosage of 0.10%. Furthermore, FE-SEM observation indicated that the GOD probably had an effect on the shape of the cement hydration products. It revealed samples containing 0.10 wt% GOD with replacement exhibited good bonding between the GOD and the surrounding cement matrix. The hydration mechanism of cement composites with GOD and replacement of cement with Silica Fume and Metakaolin needs further study. © 2018 Elsevier Ltd