In this paper, a new four-electrode sensor for fresh water conductivity measurements is presented.The measurement system includes two parts: a four-electrode conductivity sensor unit and an integrated measuring circuit. The distribution of a four-electrode in electric field and the size of four electrodes are simulated by ANSYS - the MEMS simulation tool. The prototype of the conductivity sensor, with a four-electrode (each electrode is measuring 6mm×2mm or smaller), was fabricated on a PCB. The conductivity of a tested sample could be obtained according to output of the amplifier by calibrating the voltage of the conductivity of the standard liquid. The voltages of the conductivities, in the range from 0.34V to 9.00V, are detected by an oscillograph. This test result proves that it is promising to measure conductivity of fresh water utilizing the sensor based on the four-electrode system.