Scombroid food poisoning is caused by the consumption of histamine-containing foods. Since histamine is thermally stable, controlling histamine-forming bacteria in seafood is an effective technique for limiting histamine generation. The aim of this study was to investigate the induced effects of gamma radiation on the development of histamine-forming bacteria, specifically Pantoea agglumerance, in both mackerel flesh and tryptone soya broth. Klebsiella pneumoniae, Pseudomonas fluoresense, Pantoea agglumerance, and Bacillus sp. are histamine-forming bacteria were cultured in tryptone soy broth and exposed to gamma irradiation at doses of 0.25–5 kGy. In the meantime, mackerel meat was injected with the histamine-forming bacteria and then gamma-irradiated at 0.25-5.0 kGy. K. pneumonia and Pseudomonas fluoresense were particularly susceptible to gamma irradiation, and at 1.5 kGy, they were completely destroyed. Pantoea agglumerance and Bacillus sp. were found to be more resistant, with total inactivation at 3.0 and 5.0 kGy, respectively. The D₁₀-values to inactivate 90% of the bacterial populations in tryptone soya broth and inoculated mackerel ranged from 0.13 to 1.03 kGy and 0.14 to 1.12 kGy, respectively, depending on the kind of bacteria. These findings imply that gamma irradiation can efficiently eradicate histamine-forming bacteria, lowering the risk of histamine poisoning from seafood. However, because modest doses of irradiation are ineffective in decreasing Bacillus sp, the early counts of Bacillus sp in fish samples should be closely monitored.