Lotus japonicus MG-20 seeds were exposed to space environment by space flight using a recoverable satellite. After the selection from one to three generations, several mutants were obtained。The major mutants included non-nodule mutants (18 lines) which failed to nodulate after inoculated with rhizobia for two weeks, ineffective nodulation mutants (9 lines) which had less uneven and white or transparent nodules, an abnormal leaf and flower mutant which was dwarf without stipules, abnormal flowers and less nodules, and a slender mutant with a thin stem and smaller leaves.