In this research, in using a piezoelectric material of Pb(Mg13/Nb23/)O3-PbTiO3 (PMN-PT), which has a high electromechanical coupling coefficient, we have tried to see if the material can be practically available as a new surface acoustic wave (SAW) biosensor to detect protein. As the results, the frequency filtering of the central frequency of the PMN-PT substrate is a superior result to that of the LiTaO3 (LT) substrate, but the result was not completely satisfactory. We know there is a problem in the design of inter-digital transducer (IDT) pattern. The waves transferred through the input terminal forms SAW which is sure to be transferred to the direction of the output terminal and the backward direction of the input terminal. This reflected wave is reiterated with SAW, which is transferred to the output direction, and so the frequency filtering gives a not good result. The electromechanical coupling coefficient of the PMN-PT substrate is excellent, and as such we can use it as a SAW sensor, in the near future, provided that there is a new IDT design to increase the frequency filtering.