The effect of surfactant o-phenylenediamine (OPD) on the bioleaching of marmatite with mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans was examined in shaking flasks. The effect of OPD on the iron and sulfur oxidizing capacity of the bacteria was also investigated. Results show that the addition of OPD in low concentration was favorable for the bio-oxidation of elemental sulfur and had little negative effect on that of iron. Chemical analysis and EDX analysis of the leached residues reveal that zinc was selectively leached over iron. The elemental sulfur produced from the leaching reaction was not completely oxidized and dissolved only partially even in the presence of bacteria, which limited the dissolution rate of marmatite. However, the addition of OPD accelerated the oxidation of elemental sulfur in the presence of bacteria, thus enhancing the bioleaching rate of marmatite. (C) 2008 Elsevier Ltd. All rights reserved.