We present a wireless QCM biosensor fabricated using MEMS technology. The MEMS QCM biosensor contains a 125-MHz AT-cut quartz resonator embedded in the microchannel. Because of the compact design, the MEMS QCM biosensor is suitable for mass production and device miniaturization. We performed the IgG detection measurement with different concentrations. The detection limit was l ng/mL or less, which is superior to that of the gold-standard SPR method. Furthermore, we studied the binding affinity between protein A and IgG by studying the frequency response of the QCM biosensor. It shows good agreement with reported values. Therefore, the presented MEMS QCM biosensor has advantages of compact, low cost, low power consumption, high sensitivity, and reliability.