The ion channel formation of fragment B of tetanus toxin in an artificial lipid bilayer was described.Fragment B with a molecular weight of 48000 was purified by fast protein liquid chromatography.The channel activities were recorded from an asolectin bilayer memberane by patch clamp technique.It rarely formed ion channels at neutral or acidic pHs.In contrast,with pH gradient the channel activities of fragment B were easily recorded.By analysis of single channels formed by fragment B,the conductance of the channel was 2.3pS. At different holding potentials (-100-+150mV) the channels gave same conductance, it indicated that “the fragment B channel” passed K ion in both directions. The opening-time of the channel was maintained at 20-40 and 100-120ms, and the closing-time of it was main at 20ms. These results indicated that the channel of fragment B was rapidly flickering between the states of opening and closing.