Highest direct Cr(VI) bio-reduction activity is achieved at pH 8.0. Direct Cr(VI) bio-reduction activity decreased with increased Cr(VI) concentration. Direct Cr(VI) bio-reduction rate is slower than the indirect one. Direct Cr(VI) bio-reduction at 1.0 mg Cr (VI)/L/h is demonstrated in UASB reactor. Desulfovibrio, Ochrobactrum and Anaerovorax cause direct Cr(VI) bio-reduction.