Weathering of pyrite-rich andesite has produced acid rock drainage(ARD) which causes a serious environmental problem in southeastern part of Korea. The purpose of this study is to investigate the mineralogical compositions and geochemical mobility of the heavy metals of bed rocks and the weathering products using XRD, pH measurement, XRF, SEM-EDS, ICP, and sequential extraction method. The samples from bed rocks and weathering products were collected from two sites in Yangsan area, Korea. Site 1 was excavated more recently than site 2 and site 2 was excavated quite a while ago and, therefore, has been weathered for a longer time than site1. XRD results showed that the main minerals comprising the bed rock at site 1 were quartz, chlorite, pyroxene, hornblende, and albite with minor amount of pyrite, calcite, and illite, while quartz, pyrophyllite, and pyrite were identified in site 2. Pyrophyllite and topaz were reported to be formed at higher temperature than the others identified at site 1, indicating that the bed rock at site 2 was more heavily altered by hydrothermal activity. As weathering products, a small amount of gypsum and goethite were identified at site 1(pH 2.6~7.3) and a relatively large quantity of jarosite and goethite were identified at site 2(pH 2.6~5.2). In addition, goethite was the main mineral in a gouge sample at site 2. Therefore, the different mineral compositions and pH values of samples at two different sites were supposed to be affected by the mineral composition of each bed rock and the period of weathering. The contents of heavy metals were in order of As > Zn > Cu > Pb > Cr > Ni > Cd at site 1 and Zn > As > Pb > Cu > Cr > Ni > Cd at site 2. As, Zn, Cu, and Pb were the most abundant heavy metals at these sites. The concentrations of the heavy metals at site 1 were higher than site 2 except Pb. Moreover, it is confirmed that the fraction of labile (step 1) and acid-soluble (step 2), which can be released easily into the environment, was higher at site 1. Accordingly, the weathering process at site 1 can be potentially more harmful in environment than that at site 2. However, chemical weathering is locally delayed by calcite buffering at site 1. In the case of site 2, it is expected that the heavy metals have been continuously released by low pH and the long period of weathering, although the concentrations of the heavy metals were lower than those at site 1.