Concrete pumping has been successfully adopted in modern construction. Various concrete including high-strength concrete and self-consolidating concrete can be pumped, but we still have a lack of understanding of the rheological behavior and its change during the pumping process. This study evaluates the effect of pumping pressure on the viscosity curves of cement-based materials incorporating a specific polycarboxylate. The viscosity of mortar samples increases with the pumping pressure. The viscosity increase depends on the rate of shear strain and the polymer structure of the polycarboxylate. The effect of pumping pressure is then generalized with a Sisko model. A mechanistic model for the phenomenon is discussed together with the stability potential formulated on the theory of shear-induced particle migration.