Bronze coins and mirrors which were excavated in 1987 at the Fukaya site in Kakegawa, ca 8th century, were examined by scientific methods and were treated for conservation. The following results were obtained by scientific measurements: 1) coins consist mainly of copper and of a small amount of tin, arsenic, and lead. Arsenic is generally more enriched in all coins than in Chinese bronze objects of the eastern Han and Three Kingdom Periods; 2) lead isotope ratios of the coins showed that lead used for the coins came from more than two Japanese mines; 3) qualitative analysis of two bronze mirrors by x-ray fluorescence suggested that main components were copper and tin moreover, a small amount of arsenic and lead were recognized; lead isotope ratios of corrosion product showed that lead contained in the mirrors came from a Japanese mine. The conservation treatment of the bronze was as follows: 1) cleaning by the use of soft glass-fiber, a bamboo spatula, and an ultrasonic scalpel; 2) washing with a hot stream of pure water using a Soxhlet extractor for leaching out foreign ions such as chloride and sulfate ions; 3) immersing in a solution of 3% benzotriazole in ethanol for stabilization; 4) impregnation with an acrylic resin solution (Incralac) under reduced pressure for consolidation.