The effect of gamma irradiation on the prevention of breeding a patulin-producing mold and reducing patulin content was evaluated in an apple model system. Penicillium griseofulvum, a patulin-producing standard mold strain was artificially inoculated into apples and a gamma irradiation was performed. The $D_{10}$-values of the conidia of P. griseofulvum in an aqueous suspension and the apple model system were calculated at 0.28 and 0.48 kGy, respectively. The viable cell counts of the inoculated conidia in the apples showed 2 decimal point reductions at a dose of 1 kGy. Breeding and growth of the survived conidia was prevented during 10 weeks of post-irradiation storage period, especially at $4^{circ}C$. The concentration of patulin in the non-irradiated apples was gradually increased and reached about 950 ppm at $25^{circ}C$ and 410 ppm at $4^{circ}C$, but the production of patulin was not observed during storage after 1 kGy of gamma irradiation.