Accelerating the selenite reduction rate is important in selenite bioreduction by microorganism process. This study investigates the impact of redox mediators (α-AQS, AQS, 1,5-AQDS and AQDS) on bioreduction of selenite by Shewanella oneidensis MR-1 and optimizes the bioreduction conditions with Shewanella oneidensis MR-1 and AQDS. The selenium particles obtained from cultures are analyzed using Zeta potential analyzer. The results suggest that all four tested redox mediators are able to accelerate the reduction of selenite by Shewanella oneidensis MR-1, and AQDS is the best. The optimum conditons are AQDS concentration of 0.2 mmol/L pH of 8.0 and temperature of 30 ℃. Selenite is completely removed after 48 h bioreduction by Shewanella oneidensis MR-1 with optimum conditons. Bigger size selenium nanoparticles (SeNPS) can be obtained with AQDS. AQDS may influence the composition and content of the organic layer covering around selenium nanoparticles (SeNPs). This study could provide a foundation for particle application in selenite biodegradation.