Bleeding of cement pastes is a phenomenon that can affect not only the homogeneity and stability of concrete structures, but also their durability. The aim of this paper is to deepen the comprehension of this phenomenon, especially in the presence of superplasticizer such as polycarboxylate (PCE). Bleeding of cement paste with different water to cement ratios including low and high PCE dosages is measured using Turbiscan device. The results show that the evolution of bleeding is strongly modified by the presence of PCE. The bleeding capacity increases with PCE dosages, but the time at which the bleeding reaches a constant value also increases with PCE dosage. In order to understand the effects of PCE on cement paste bleeding, additional tests were performed including rheology, isothermal calorimetry, and indirect permeability assessment using bleeding test. So, it appears that the effect of PCE could be explained by interdependent mechanisms: the release of water trapped between agglomerated particles, retardation of cement hydration, and localization of bleeding leading to modification of permeability.