For the preparation of non-infective vaccine against typhoid fever, the authors had carried out an investigation on the possibilities of using $^{60}Co;{gamma}$-ray irradiation for the inactivation of Salmonella typhi Ty 2. The following results were obtained. 1) Chicks shortly after hatching were higher susceptible than mice to intracerebral injection with S. typhi. 2) In safety test on experimental animal, $^{60}Co;{gamma}$-ray irradiated vaccines demonstrated no clinical symptom while the phenol treated vaccines revealed several cases of narcosis by intraperitoneal injection in chicks. 3) The rabbit antisera immunized with $^{60}Co;{gamma}$-ray irradiated and phenol treated vaccine revealed almost same agglutinin titers to each other. 4) In potency test in chicks, there was no significance in the protective capacity between $^{60}Co;{gamma}$-ray irradiated and phenol treated vaccines.