We herein describe a novel washing-free electrochemical strategy for target DNA detection by utilizing the peroxidase mimicking DNAzyme. The DNAzymeincorporated DNA probes, the key components of this strategy, are designed to be not able to form G-quadruplex structure in the initial state such that the peroxidase mimicking activity of DNAzyme is kept suppressed. The DNAzyme sequences, however, would be converted to the catalytically active G-quadruplex structure by the presence of target DNA, whose peroxidase mimicking activity then promote the precipitation reaction of 4-chloronaphthol (4-CN) on the electrode. Due to the precipitates produced on the electrode surface, the electrochemical reaction between the redox materials and electrode surface is inhibited, consequently leading to a significant increase of the impedance signal. Based on this novel electrochemical design principle, we successfully detected the target DNA from sexually transmitted disease (STD) pathogens such as Chlamydia trachomatis, Trichomonas vaginalis, and Herpes simplex virus type 2 in real patient samples, verifying its practical diagnostic capability in the clinical applications.