Introduce the classfication, structure, function and application of biological fixation of nitrogen. The course contents included are：global nitrogen cycle, classification of nitrogen fixation microorganism, isolation of microorganism, classification of symbiosis between Rhizobium and legumes, Rhizobium infection process and nodule formation, property and synthesis of leghmoglobin, nitrogen fixation capacity of bacteriod, nitrogenase and electrontransport system, nodule types and nitrogen fixation in non-legume, symbiotic nitrogen fixation in cyanobacteria, nitrogen fixation in rhizosphere of higher plant, inoculation of Rhizobium, measurement of nitrogen fixation, application of stable isotope in nitrogen fixation.