Selenium(Se) is one of the important and essential trace elements in human body,but the range between biological activity and toxicity of Se is extremely narrow,so it's easy to show its toxicity.However,Se(0) nanoparticles have an advantage of high security and strong efficiency.In this experiment,LA4 strain with higher tolerance to sodium selenite was selected from lactic acid bacterias in our laboratory.We found that 46.79% of 4 mmol / L Na 2 SeO 3 was reduced by spectrophotometry.We also found LA4 strain could reduce sodium selenite into red elemental selenium by transmission electron microscope(TEM) and X-ray photoelectron spectrometer(XPS) test.We could see a large number of particles from transmission electron microscope pictures of Na 2 SeO 3,some of the particles sticked to the cell surface,but some of the particles were free in the culture medium,their diameters were mainly in the range from 50nm to 200nm.