In this chapter, the theoretical concepts of magneto-rheology control in extrusion-based three-dimensional (3D) concrete printing are first illustrated. Based on the fact that some residual magnetic clusters exist in cementitious suspension after removing external magnetic field, a conceptual examination of the application of magneto-rheology control to 3D printing is presented by rheological experiments on cementitious paste with nano-Fe3O4. It is revealed that a faster structural build-up is observed compared to the situation without magnetic field. This finding offers an innovative methodology to actively improve the buildability of 3D printed concrete by introducing a short-pulsed magnetic field during extrusion. Further research regarding the print head design for magneto-rheology control of 3D concrete printing is prospected.