A probe (1) for measuring the conductivity of a solution comprises a hydraulic part and an electronic part; the hydraulic part comprises a conduit (2) in the shape of a double tuning fork having an inlet (3) and an outlet (4) for the solution whose conductivity is to be measured; the electronic part comprises an energizing toroidal coil (7) and a receiving toroidal coil (22), both fitted round the conduit (2); the receiving coil (22) is mutually concatenated with the energizing coil (7) through an electromagnetic flux (F) generated by the energizing coil (7) in the respective toroid (T1) and through the solution circulating in the conduit (2); the probe (1) also comprises a feedback circuit (111) to keep the electromagnetic flux (F) constant.