In this paper, a persistent-current method for measuring critical characteristic curves of superconductors has been described. In comparison with the usual four-probe method, this new method possesses the following advantages: (1) The Ic (H) curves thus determined have clear physical significance. (2) The technical difficulty of introducing heavy current into the cryostat is avoided. (3) There is no danger of burn-out of the specimen tested.The Ic(H) curve of cold worked niobium wire has been determined with this method. The result confirms the existence of the peak in the Ic (H) characteristic observed previously with the four-probe method.