A snow tunnel is often formed between the water surface of a small stream and the base of a snow cover in snowy areas. Observations made in northern Japan revealed that the amount of snow ablated at the ceiling of the snow tunnel ranged widely from 1.3 - 50 kg/m2d. This amount was calculated using heat transfer method; assuming that the ceiling was ablated only by the flux of heat from stream water, the amounts observed and calculated were found consistent.