We investigated the effect of hydrogen on the electrical resistance of melt-spun amorphous alloys. It was found that Mg-based amorphous alloys show the increases in the electrical resistance when they are immersed in hydrogen-dissolved water and that the electrical resistance increases by hydrogen absorption and returns to the initial level by hydrogen desorption. These results show the possibility that the Mg-based amorphous alloys may be applied to hydrogen sensing materials in water.