The attenuation of Stoneley waves by an open borehole fracture is closely related to fluid flow in the fracture. We consider the dynamic response of a viscous fluid in a borehole fracture to the oscillating pressure excitation of Stoneley waves at the fracture opening. A dynamic model has been developed to describe the fluid motion in the fracture. This model relates both viscous shear effects at the fracture surface and the acoustic wave propagation in the fracture fluid. The dynamic conductivity is derived to characterize the fluid conduction through the fracture. This model is applied to study Stoneley wave attenuation across a horizontal and along a vertical borehole fracture. In the horizontal fracture case, the theory is found to agree with laboratory fracture modeling data after minimizing scattering effects due to the fracture. In the vertical fracture case, where the scattering effects are minimal, the theory is in excellent agreement with the laboratory data. ¿ American Geophysical Union 1989