In this paper we report a new method for determining the size of flaws using the zeroes in the real and imaginary parts of the ultrasonic scattering amplitude [1]. It is observed that, for a wide class of flaws, the wavenumbers or frequencies at which the real and imaginary parts of the scattering amplitude go through zero are closely related to the flaw dimension in the scattering direction. This relationship remains remarkably stable for different interrogation directions and thus may serve as a basis for flaw sizing and reconstruction. In the decomposition of the scattering amplitude into its real and imaginary components, this method requires that the phase reference (or the “zero of time”) be placed at the centroid of the flaw. In many respects the method of flaw sizing using the zeroes is similar to the one-dimensional version of the inverse Born approximation (1-D IBA) [2], In fact, it employs the same input data as the 1-D IBA and consequently also shares certain common limitations such as the sensitivity of the sizing results to the zero of time determination and the available bandwidth of the scattering data [3,4]. However, flaw sizing using the zeroes is simpler and more straight forward because the sizes are obtained directly from the frequencies where the zeroes occur.