A method for measuring the conducting fluid saturation and the resistivity of a porous medium have application to development of underground geological formations. A solid sample is extracted from the medium and placed in a centrifugation cell, beside a second sample for limiting the capillary in the first sample. The two samples are partly desaturated by subjecting them to centrifugation. The resistivity of the sample is measured by placing it in a radial-electrode resistivity measurement cell. The saturation of the sample is then determined by measuring its nuclear magnetization by means of an NMR device. Repeating this procedure for different centrifugation velocities provide resistivity and saturation pairs allowing a relationship between saturation and resistivity to be estimated.