The failure of polycarboxylate ether (PCE) superplasticizers to adjust the workability of cement paste containing clay is due to the stronger adsorption of PCE to clay than cement particles. This study aims to develop a novel sacrificial agent (SA), ionic liquids (ILs), for PCE to make it more compatible in cement paste containing clay. Firstly, effect of ILs on fluidity of cement paste containing clay is investigated and the results show that ILs composing of long chain imidazolium-based cation make PCE more compatible in cement paste containing clay, leading to the improved fluidity of cement paste by 70%. NMR, XRD and zeta potential measurements indicate that ILs is preferentially adsorbed on clay by electrostatic attraction and free PCE to disperse cement particles again. The mechanism behind is that the addition of ILs is effective to hinder the hydration and swelling of clay by preferential electrostatic adsorption, so that the interlayer spacing of clay will not be accessible for PCE intercalation. In conclusion, ILs is an excellent clay-specific SA candidate to improve the tolerance for clay of PCE as a superplasticizer in cement paste.