Enterobacter sakazakii is an emerging foodborne pathogen that has caused several cases of meningitis and necrotizing enterocolitis in infants and has been associated with infant formulas. Five strains of E. sakazakii were inoculated individually into brain heart infusion broth and rehydrated or dehydrated infant milk formula and exposed to ionizing radiation. E. sakazakii strains in brain heart infusion broth and rehydrated infant milk formula (RIMF) were exposed to irradiation dose of up to 1 kGy while strains in dehydrated infant milk formula (DIMF) were exposed to irradiation dose of up to 9 kGy. The D(10)-values were determined by using a linear regression model. Average calculated D(10)-values ranged from 0.21 to 0.29 kGy, 0.24 to 0.37 kGy, and 1.06 to 1.71 kGy in brain heart infusion broth, RIMF, and DIMF, respectively. The results obtained from this study will be useful for powdered infant milk formula industries to reduce the risk associated with E. sakazakii.