This study investigates the effect of adding a small concentration (0–0.5 wt. % addition by mass of cement) of graphite nanoplatelets (GNP) to cementitious materials. GNP-water-surfactant suspensions with various surfactant concentrations (0–20 mg/mL) and sonication times (0.5–6 h) are prepared and subjected to different protocols (long-term standing and centrifugation). Then, dispersion and stability are qualitatively observed through digital imaging and scanning electron microscopy after long-term standing and quantitatively evaluated by calculating the absorbance spectra ratio. Furthermore, the mechanical properties of GNP-reinforced cement (GNPRC) are investigated. The results show that 8 mg/mL and 4.5 h are the best choices for the surfactant concentration and sonication time, respectively. Also, obvious reinforcement for the mechanical properties of GNPRC is found; specifically, the 0.05 wt. % addition of GNP increases the compressive strength by 7.5 % and 16.7 % after 7 days and 28 days curing, respectively. Then, between the GNP dosages of 0 and 0.5 wt. %, the flexural strengths at 7 days and 28 days continuously increase, up to 55.6 % and 53.3 %, respectively.