In order to find the optimum condition for measuring the explosion limits of flammable gases by using metal wire fusing as the ignition source, the explosion limits of the methane/air system have been measured under various conditions in a bell jar type vessel of volume 3 dm(3). Metal wires used were of copper, Nichrome, platinum, molybdenum and tungsten, with diameters ranging from 0.3 to 1.0 mm. Fusing was made by 12, 24, 36 and 48 V of direct current (DC), and also by 100 V of alternating current (AC). With these experiments, the effect of ignition abilities on explosion limits measurement has been made clear. As a result, it has been found that the fusing of metals of relatively high melting point, such as molybdenum, with a relatively high electric voltage, e.g., DC 36-48 V, is suitable for the explosion limit measurement. The explosion limits of methane in air have been determined to be 4.7-16.3%.