15 pieces of copper artifacts of Siba Culture unearthed from Donghushan site (1800 B.C.) in Gansu province were examined. 8 of them were analyzed by atom absorption spectrographical analysis, and 11 of them were examined under microscope and scanning electron microscope. The results shown that arsenic(As) as major element was in the 11 pieces of copper artifacts which ranged from 2% to 8%, and all of them were manufacturing by hot forging, some followed by cold working. This kind of materials has a better mechanical properties then pure copper. It is the first time to find arsenic copper artifacts in such large amount in China. The site of Donhuishan was located in the northern slope of Qilian Mountain where nonferrous metal ores are in abundance, including copper-arsenic ores which could be used to produce arsenic-copper alloy.