The thermophilic archaean, Acidianus brierleyi, was examined for its feasibility to bioleach copper from a low-grade chalcopyrite ore (1.11-1.44% copper and 20.6-23.7% iron) obtained from IOCG deposits. The chalcopyrite leaching at 65°C and pH 1.8-2.5 was markedly accelerated in the presence of A. brierleyi, and an extremely high 80% leaching of copper in the low-grade ore (25-38 μm particles) was achieved in 14 days in a batch stirred reactor. By comparison, only a slight 5 % iron was leached out in 14 days in the presence or absence of A. brierleyi. In other words, A. brierleyi selectively leached chalcopyrite, while the bioleaching of magnetite as a gangue mineral was negligible. Moreover, bioleaching of the low-grade ore (53-75 μm particles) yielded 55% copper recovery after 20 days of operation in a column reactor. The good results for the copper bioleaching in the column reactor are very similar to those in the stirred reactor. These results lead to the conclusion that the thermophile bioleaching with A. brierleyi is attractive as an economical and environmentally friendly process for good copper extraction from low-grade chalcopyrite ore.