Axial Seamount is a large, active, ridge axis volcano located on the central segment of the Juan de Fuca Ridge in the northeast Pacific Ocean. Magnetotelluric (MT) data have been collected at three sites, approximately 4 km apart around the eastern rim of the volcano, during a 65-day deployment. MT responses, in the bandwidth of 102--105 s, are almost isotropic, with a weakly-defined principal direction of strike parallel to the main topographic trends of Axial Seamount, and are relatively flat over the whole bandwidth. Apparent resistivities are of the order of 7--20 &OHgr;m, and phases are as low as 30¿ at the short periods. Diagonal terms of the MT tensor are an order of magnitude smaller than the off-diagonal terms, suggesting that three-dimensional effects on the data are minimal. Two-dimensional inversions suggest that seafloor bathymetry and the distant coastlines have a surprisingly small effect on the MT response, and one-dimensional inversions fit the MT data to within the errors with no serial correlation in the residuals. A low crustal resistivity is the most robust part of the model, probably due to seawater in fractures and possibly due to a magma chamber. An electrical asthenosphere, although less well constrained, exists over a depth range 30--60 km, and the resistivity of this region is compatible with about 8% fraction of melt. ¿ American Geophysical Union 1996