Penicillium expansum causes the accumulation of patulin in apples, which has a negative impact on food safety and human health. Higher levels of polyphenols such as flavan-3-ols, flavonols, procyanidins, dihydrochalcones and phenolic acids in traditional apple varieties showed a high potential for resistance to infection by P. expansum. On this basis, the resistance of selected traditional apple varieties, ´Ilzer Rosenapfel´, ´Bobovec´, ´Mašanka´ and ´Zelenika´, to infection by P. expansum was analysed after harvesting in 2022, and after a six-month storage period. The samples of each examined traditional apple variety were analysed using the HPLC-PDA method to determine the polyphenol profile. To investigate the resistance of the traditional apple cultivars to P. expansum infection, 1 cm thick apple slices were first sterilised in Petri dishes, then inoculated with 14 days-old P. expansum CBS 325.48 slices and incubated in at 29°C until the P. expansum colony on the apple disc reached a diameter of 9 cm. The patulin content was determined using the LC-MS/MS method of Sulyok et al. (2020). The results showed that ´Ilzer Rosenapfel´ had the highest content of procyanidin B2 and phloridzin after six months of storage, ´Mašanka´ had the highest content of chlorogenic acid, procyanidin A2, catechin, and rutin, ´Bobovec´ had the highest content of procyanidin B1 and epicatechin and ´Zelenika´ had the highest content of p-coumaric acid. The average growth period of the P. expansum colony to reach a diameter of 9 cm was from 5 to 8 days. Furthermore, the results showed that patulin was only detected in ´Ilzer Rosenapfel´. Also, ´Ilzer Rosenapfel´ showed the highest content of epicatechin, gallic acid and catechin, which contributed to the increase inpatulin concentration in the tested variety. This only adds to the confirmation of the fungal sensitivity to cellular oxidative status perturbations, as well as to confirmation of the polyphenolic compounds' prooxidative activity in the examined ´Ilzer Rosenapfel´ traditional apple variety.