Abstract: This paper presents a highly efficient absorbing boundary condition suitable for use in the finite-difference time-domain (FDTD) modeling of acoustic fields. The new method seeks a least square estimate of a transfer matrix for field components near truncating boundaries by means of matrix pseudoinversion. The resulting absorbing boundary is considerably more effective than a number of existing ones. The method is also computationally economical and robust. The performance of the new method is demonstrated by numerical experiments on a point-source radiation problem, a wedge diffraction problem, and a scattering problem in which a plane wave is scattered by a circular cylinder.