In this work, a sensitive DNAzyme-based electrochemical sensor had been developed for Pb2+ detection with platinum nanoparticles decorated TiO2/α-Fe2O3 composite as signal labels. The morphological and compositional properties of the PtNPs/TiO2/α-Fe2O3 were examined by using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The result showed that the shape of α-Fe2O3 nanocrystals were the cubic, the average length ranged from 150 to 300 nm, and the PtNPs with about 3–4 nm in diameter were well dispersed on the surface of TiO2/α-Fe2O3. TiO2/α-Fe2O3 were used as a “carrier” to load the PtNPs tracers as well as for Apt3 immobilization. In turn, the DNAzyme structure of Apt1 and Apt2 was immobilized on the gold electrode surface as the capture probes. Subsequently, DNAzyme modified electrodes reacted with target Pb2+ and the Apt3/PtNPs/TiO2/α-Fe2O3 composite were deposited on the electrode surface. The performance of the DNAzyme-based electrochemical sensor was tested by recording the electrocatalytic reduction current toward H2O2. Enhanced sensitivity was achieved by TiO2/α-Fe2O3 nanocomposites as a nanocarrier in order to PtNPs at a high ratio. The DNAzyme-based electrochemical sensor described here exhibited excellent sensitivity and specificity for target ion. This work represented a promising potential for on-site testing Pb2+ in real drinking water and serum sample analysis.