The conventional medical immunoassays (ELISA/CLIA/FPIA) are not only costly (>10,000 USD), large in size (>10,000 cm3), but also require a vast number of sampling (25 £gL/well ¡Ñ 12 well) and long detection time (1~2.5 hr). To develop a biomedical microsensor for the application of portable detecting microsystem, this thesis proposes a flexural plate wave (FPW) microsensor with a novel reflection grating electrode (RGE) microstructure. Comparing to the conventional acoustic microsensors, the FPW based device has higher mass sensitivity, lower operation frequency but higher noise level. To overcome this disadvantages, this study added the RGE microstructure into the design of FPW sensor and investigated its influences on the reduction of insertion loss and noise level. By using the surface and bulk micromachining technologies, this thesis designed and fabricated FPW-based mass-sensing device with a small volume of 0.189 cm3 and a novel RGE microstructure. The main processing steps adopted in this research include six photolithoghaphies and nine thin-film depositions. In this work, a high figure-of-merit C-axial orientation ZnO piezoelectric thin-film was deposited by a commercial magnetic radio-frequency (RF) sputter system. On the other hand, the gold/chrome interdigital transducer (IDT) and RGE aluminum electrode were deposited utilizing a commercial E-beam evaporator system. For the optimization of design specifications of the FPW devices, the space of input and output IDTs, pair number of IDT, length of delay line gap and with/without RGE design were varied and investigated. Under the optimized IDT specification, the FPW microstructure presents lower central frequency (2¡ã4 MHz), insertion loss (-11 dB) and noise level (<-30 dB) than that of the FPW based microsensor without RGE microstructure. In addition, as the sampling volume of the testing DI water is equal to 1 £gL, a high mass sensitivity (-48.3 cm2/g) and short responding time (5 min) of the FPW microsensor with RGE design can be achieved in this work. The excellent characteristics mentioned above demonstrated the implemented FPW microsensor is very suitable for the applications of portable biomedical detecting microsystems.