A bacterium strain QZB-1 with high selenite reduction efficiency was isolated from Se-rich soil in Qinbei District of Qinzhou City, Guangxi Province. The strain was identified as Serratia marcescens through 16S rDNA gene sequence analysis. The results revealed that the strain could tolerate selenite concentration as high as 180 mmol/L. Further study suggested that the strain QZB-1 could reduce 95% of 1 mmol/L selenite within 36 hours, and selenite reduction rate decreased with the increase of selenite concentration. The orthogonal experiment indicated that the rank of influence degree by selenite reduction was initial selenite concentration > incubation time > inoculum. The optimal conditions for selenite reduced were as following:initial selenite concentration 1 mmol/L, inoculation volume 10%, and incubation time 36 hours. Under these conditions, selenite reduction rate was more than 98.55%. The findings suggested that the novel selenite reducing strain Serratia marcescens QZB-1 can efficiently reduce selenite to elemental selenium nanoparticles, and can be effectively applied in the bioremediation of selenite polluted soil and water.