Under room temperature the electron spin resonance （ESR） spectrometer was used to study the free radical formation in antibiotic-producers （e.g. Streptomyces ribosidificus

Streptothyces kanamyceticus and the phage-resistant culture of Streptomyces kanamyceticus） in order to investigate antibiotic-producer mutagenesis breeding induced by N ion implantation.The results show that a great number of free radicals can be induced by N ion implantation and the yields increase with implanting dose. The death rate of antibiotic-producers also rises due to the increase of the free radical yields.