In recent decades, considering environmental issues, partial replacement of Portland cement with supplementary cementitious material (SCM), namely ground granulated blast furnace slag (GGBS), has been in the spotlight of research. On the other hand, carbon‐based nanomaterials, especially graphene oxide (GO), are recognized as an extraordinary additive with special characteristics that can be included in cementitious materials. In this research, the impact of GGBS on the mechanical properties and durability of GO‐modified mortars was investigated at 28 and 90 days. The results demonstrate that by increasing the content of GGBS, a decrease in the flexural and compressive strength compared to plain cement sample was seen. On the other hand, incorporation of GGBS and GO led to higher strength compared to GO‐cement mortar. Also, the compressive strength of the sample containing 20% GGBS and 0.03% GO was 38.7% higher than the plain cement sample at 90 days. On the other hand, adding GGBS to a GO‐reinforced sample resulted in a more durable specimen against chloride and acid environments. The sample made of 40% GGBS in GO‐modified mortar not only has the best efficiency in harsh environments but also has the lowest water absorption. This mortar improved the migration coefficient, mass loss in HCl solution, and initial sorptivity by 20.1%, 57.7%, and 37.1%, respectively. Moreover, the mentioned sample had a denser microstructure with smaller cracks compared to other samples, based on scanning electron microscope (SEM) images.