Abstract: The indirect boundary element method (IBEM) is proposed to study the three-dimensional scattering problem by a two-dimensional valley embedded in a fluid-saturated, poroelastic layered half-space for obliquely incident seismic waves. The wave-number transform is applied in the axial direction of the valley to reduce the three-dimensional problem to a two-dimensional plane strain problem. Then the dynamic problem is solved in one section perpendicular to the axis of the valley, and finally the three-dimensional responses of the valley and of the layered site are obtained through the inverse wave-number expansion. The validity of the method is confirmed by comparison with the results of the corresponding dry poroelastic case, and numerical calculation and analyses are performed by taking the amplification of obliquely incident plane waves by an alluvial valley in a uniformly saturated poroelastic half space and in a single saturated poroelastic soil layer overlying on elastic bedrock as examples. The results show that the three-dimensional responses are distinctively different from the two-dimensional responses, that the surface displacement amplitudes near the valley in dry poroelastic and saturated poroelastic half-spaces are very different, and that the displacement amplitudes around the valley in a uniform saturated poroelastic half space are obviously different from those in a saturated, poroelastic layered half-space.