Abstract: There exist different δ~(15)N values in shoots of different species and varieties of leguminous grasses, showing that the potentialities of their dinitrogen fixation were apparently different. The δ~(15)N values in shoots of some grasses tested were too low, and very close to δ~(15)N value of atmospheric N_2 (0‰). It is possible that they get N to meet the needs of their growth through some associative dinitrogen fixation processes. Further study should be done.