Abstract:The Longqiding ancient casting site locates at top slope of Longqiding hill in Luya village, Longan town, Xingye county, Yulin city, Guangxi Zhuang Autonomous Region. Remain areas of the site exceed 10 000 m2. From 2020 to 2021, the authors conducted many field surveys, collected samples and archeological typology of moulds unearthed from the site. Composition and microstructure of 12 samples of casting slag, cast iron and pottery moulds from Longqiting ancient casting site are analyzed and examined with X-ray fluorescence, metallographic microscopy, and mineralographic microscopy. The results show that main products of the site are iron wok and iron kettles. Casting slags are high-iron slags of Fe-Si-Mn-P with are some cast iron prills in slags. Microstructure of cast iron is mainly ledeburite, with composition of Fe-Si-P-Ni alloy. Clay moulds are usually made of at least three layers of clay stacked on together. The inner layer of mould is the finest and intentionally combined with plant ashes. The middle layer of mould is made of fine silt mixed with rice husks; the outer layer of mould is made of coarse-grained silt and mixed with rice husks. The inner surface of mould contains Zr heat-resistant protective material.