The most extensively used construction materials in the world are cement, mortar, and concrete. GGBS is an alternative to Portland cement that can reduce carbon dioxide emissions significantly and has been recognized as an environmental-friendly construction material. It can also be used as a substitute or as a supplementary to cement, which can help promote sustainable development globally. On the other hand, 3D printing concrete is a revolutionary concrete building process that is developed by many research institutes and companies across the world. Some of the benefits of 3D printing concrete are the use of materials is optimized, reduce labour cost, fast construction and able to construct customized buildings. However the study about 3D printing concrete materials needs more extensive works in order for the materials to fulfill the criteria of 3D printing concrete properties. Therefore, this study tends to explore some of the materials properties of 3D printing concrete. The objective of this study is to investigate the fresh properties and flexural strength of 3D printing concrete containing GGBS as partial cement replacement and to evaluate the optimum percentage of GGBS as partial cement replacement in 3D printing concrete. The percentage replacement of GGBS that was carried out in this study was 0%, 20%, 30%, 40%, and 50% with a 0.5 w/c ratio. Extrudability, flowability, buildability, and flexural strength tests were performed. From the experimental results, it shows that 30% of GGBS replacement recorded the highest flexural strength. The mix also performs well in extrudability and buildability test.