The series piezoelectric quartz crystal (SPQC) sensor is widely used for detecting microorganisms. However, because of the slight corrosion of metal electrodes in ammonia-containing media, the SPQC is unsuitable for the detection of urease-producing bacteria. In this paper, a molecular wire piezoelectric urease-producing bacteria (MWPUB) sensor was proposed for rapid identification and quantification of urease-producing bacteria. A polyimide–polypyrrole composite film was used as an electrode in place of the original metal electrode in SPQC and connected to a piezoelectric quartz crystal in series in a self-made oscillator. The composite film could react with NH₃, which caused a decrease of conductance and resulted in a change in oscillating frequency of the piezoelectric quartz crystal. When the MWPUB sensor was used to quantitatively determine urease-producing bacteria, the frequency detection time (FDT) obtained from the frequency shift curve had a linear relationship with the logarithm values of the initial concentration of urease-producing bacteria in the range of 8 to 3.2 × 10⁸ colony forming units (cfu) per millilitre (mL). Compared with SPQC, the new method was sensitive, rapid and stable in culture media.