In order to study nitrite degradation mechanism of Lactobacillus plantarum L5,its ability to degrade nitrite,protein expression and bacteria morphology in the presence of nitrite were studied using N-( 1-naphthyl) ethylenediamine dihydrochloride method,sodium dodecyl sulfate polyacrylamide gel electrophoresis,and scanning electron microscope respectively. Results showed that the nitrite degradation rate was 56. 25% after fermentation under normal conditions for 36 h. When the p H value was retained at 6. 8 and the acid degradation was eliminated,the nitrite degradation rate was 70. 59%. In the presence of nitrite,L5 could secrete protein A with molecular weight about 200 k Da. Furthermore,expressions of protein B with molecular weight about 50 k Da,protein C with molecular weight about 40 k Da,protein D with molecular weight about 34 k Da were all improved. L5 could still grow in the culture medium with nitrite as the only nitrogen source,but the existence of nitrite changed its shape.