An electrochemical sensor incorporating a signal enhancement for the determination of lead (II) ions (Pb2+) was designed on the basis of the thrombin-binding aptamer (TBA) as a molecular recognition element and ionic liquid supported cerium oxide (CeO2) nanoparticles–carbon nanotubes composite modification. The composite comprises nanoparticles CeO2, multi-wall carbon nanotubes (MWNTs) and hydrophobic room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). The electrochemical sensors were fabricated by immersing the CeO2–MWNTs–EMIMBF4 modified glassy carbon electrode (GCE) into the solution of TBA probe. In the presence of Pb2+, the TBA probe could form stable G-quartet structure by the specific binding interactions between Pb2+ and TBA. The TBA-bound Pb2+ can be electrochemically reduced, which provides a readout signal for quantitative detection of Pb2+. The reduction peak current is linearly related to the concentration of Pb2+ from 1.0×10–8 M to 1.0×10–5 M with a detection limit of 5×10–9 M. This work demonstrates that the CeO2–MWNTs–EMIMBF4 nanocomposite modified GCE provides a promising platform for immobilizing the TBA probe and enhancing the sensitivity of the DNA-based sensors. Keywords: Electrochemical, DNA-based sensor, Lead (II) ion, Ionic liquid, CeO2 nanoparticle, Multi-wall carbon nanotubes