The surface acoustic wave (SAW)-impedance sensor, which is composed of a 61 MHz SAW resonator and a pair of parallel platinum electrodes, has been successfully applied to rapid detection of glycine (G1y), L-arginine (L-Arg) and L-aspartic acid (L-Asp) and is reported in this paper. Two methods are described — the calibration curve method and the frequencimetric titration method. The effect of formaldehyde solution on the frequency shift is discussed. For the calibration curve method: in unpretreated formaldehyde medium, the detection limit of G1y, L-Asp, L-Arg is 1.40×10−5M, 1.48×10−6M, 1.04×10−5M and the frequency shift is linear up to 1.83×10−3M, 1.60×10−3M, 1.37×10−3M; in pretreated formaldehyde medium, the above values are 7.85×10−6M, 1.11×10−6M, 2.30×10−6M and 1.53×10−3M, 1.51×10−3M, 0.96×10−3M, respectively. Using the frequencimetric titration method, the lowest titratable concentration of G1y, L-Asp, L-Arg is 1.14×10−5M, 1.07×10−5M, 1.70×10−5M. A comparison study between the SAW method and some other previously reported techniques is discussed in this paper.