A sensor using a single monomode low-birefringence (Lo-Bi) fiber for simultaneous measurement of current and voltage has been designed, which uses Faraday effect for detection of current and Kerr effect for detection of voltage. Theoretical analysis shows that the current component can be measured free from the influence of the voltage component, and the two components can be easily separated. Experimental results demonstrate the feasibility of voltage sensing based on the Kerr effect of Lo-Bi fiber, which is the main point in this proposal.