To investigate microbial mediated As release and mobilization in the high arsenic groundwater, indigenous iron/As reducing bacteria were isolated from high arsenic groundwater in the Hetao Basin of Inner Mongolia in China. These isolates were identified to be Fe(III) and As(V) reducing (IAR) Shewanella putrefaciens IAR-S1, Fe(III) reducing (IR)S.xiamenensis IR-S2 and Klebsiella oxytoca IR-ZA, and As(V) reducing (AR)Citrobacter freundii AR-C1, Paralostridium bifermentans AR-P1, Klebsiella pneumoniae AR-K1 and Aeromonas hydrophila AR-A1. The incubation results showed that strains IAR-S1, IR-S2 and the control S. oneidensis MR-1 reduced ferrihydrite quickly and re-immobilized As. Strains AR-C1, AR-P1, AR-K1 and AR-A1 reduces As(V) to As(III), and arsenic (As-tot) was released into the aqueous phase with strain IR-ZA and strain AR-C1.