Laboratory experiments were used to investigate the effects of initial pH and applied potential on the growth of Leucobacter sp. Ch-1 and Cr (VI) reduction and establish the pH-Eh diagram for Leucobacter sp. Ch-1-Cr-H2O system. The results showed that the preferred initial pH for Leucobacter sp. Ch-1 growth was from 7.0 to 11.0. At this pH range, 56.2-99.5% of Cr (VI) was reduced by Ch-1 strain. The applied potentials from -700 to 0 mV, from -800 to +300 mV and from -800 to +400 mV at 7.0, 9.0 and 11.0 of initial pH values were favorable for the bacterial growth. The corresponding ranges of applied potentials for bio-reduction of Cr (VI) were from -200 to 0 mV, from -800 to +200 mV, and from -700 to +100 mV at above initial pH values. In the potential-pH diagram, the region of initial pH and Eh for Cr (VI) bio-reduction was included in the region for Leucobacter sp. Ch-1 growth and the stable region of Cr(OH)3, which implied that Cr (VI) could be reduced to trivalent chromium existing in the forms of Cr(OH)(3) precipitate under the presence of Leucobacter sp. Ch-1 in alkaline condition. The results suggest that Leucobacter sp. Ch-1 has potential application for remediation of Cr (VI) contamination sites. (C) 2008 Elsevier B.V. All rights reserved.