The plasma current is modulated with an alternating current (ac) component in a frequency range of 90 Hz 900 Hz in the plateau discharge phase in the CT-6B tokamak. *4 plasma electric conductivity profile in a form of (1 -,'/a2)" with a parameter a , which is fitted with the experimental data, can be determined. The effects of magnetic shear in a tokamak field configuration on the current penetration are taken into account in the numerical simulation. The measurement method and obtained results are discussed.