Fog might play an important role in the water balance in foggy regions. We measured the amount of fog deposition (deposition of fog and dew waters) using lysimeters in a flatland mire on the Pacific coast of eastern Hokkaido Island. During five observed nights, summer fog was observed on four nights: one night had advection fog and three nights had radiation fog. The amount of advection-fog deposition per night was 0.6 mm on average, reaching 20 of the daily evapotranspirative water loss from this mire. This value suggests that the advection-fog water supply is not negligible. In contrast, the amount of radiation-fog water supply per night was much smaller than the other terms of water balance such as rainfall and evapotranspiration, indicating that the amount of radiation-fog deposition is negligibly small.