Patulin is a food mycotoxin which induces genotoxicity and acute intestinal disease in infants. Patulin mainly originates from fruit putrefactive moulds, especially in apples, which necessitates the maintenance of strong safety standards against patulin for fresh and processed apples. To investigate the patulin producing moulds in Korean apples, 16 morphological types of fungi were isolated from Korean apples and a patulin producing fungus was identified based on a sequence analysis of the region of internal transcribed spacers (ITS5-5.8S-ITS4 region, 505 base pair) and the 26 rRNA D1/D2 region (527 base pair). Morphological analyses were also performed. The isolated patulin producing fungus was found to a representative species of Penicillium crustosum. The maximal patulin production ability of the isolated fungus (P. crustosum) and the patulin producing standard strain (P. griseofulvum, ATCC 46037) in an SY broth medium were 0.32 and 2.46 mg/L, respectively.