Toshogu shrine, Futa-arasan shrine, and Rin-noji temple were constructed at Nikko, Tochigi prefecture in 1615-1654. In the precincts of these two shrines and one temple there are 110 buildings designated as national treasures and important cultural properties of Japan. Since the area has a moderate temperature and high humidity in summer, and low temperature with heavy snow in winter, various forms of deterioration have been found in the buildings. Therefore, these buildings have been reconstructed and/or repainted whenever necessary. This report on the conservation studies of these buildings, by the office of restoration of cultural properties in Nikko, 1974-1986, discusses: lacquering techniques of the Niten-mon gate, Daiyu-in; research on the chemical causes for and countermeasures against the blackening phenomenon on lacquered buildings microbiological research on the blackening phenomenon; comparative experiments on some antiweathering films of lacquer; research on irregular discoloration found in <i>toyu-saishiki</i> on the fence of Toshogu shrine; research on preventive methods for fungal growth on paintings on buildings; investigation of biodeterioration in 16 buildings; and a five-year survey of the climate around the buildings.