It was clarified that the high ability of rhizobia to reduce the greenhouse gas(GHG) N2O is due to high expression of the nosZ gene that converts N2O to N2. Also, by inoculating helper microorganisms into soybeans in which N2O-reducing rhizobia coexist, symbiotic nitrogen-fixing activity by N2O-reducing rhizobia and improvement in the growth of soybean were observed.