The isolations of fungi were observed, the isolations which were of rotting apples, pears, pine-seeds and dates cultivated in Korea, while they were living upon them. As a result of such observation. Penicillium sp. which rotted apples and pears could be isolated from the apples and pears. When the Penicillium sp. was inoculated into some fresh apples and pears, they were all rotted away. This fungus was identified as Penicillium expansum. Some fresh apples and pears inoculated with a mass of mycelium and conidia of P. janthinellun or some others inoculated with those of P. frequentans were not rotted. Though the P. expansum has been known to us a destructive not of pomaceous fruits, this fungus strain also caused the putrefaction of pears. It was found that P. expansum could be properly grown up at the temperature of $25^{circ}C$ and pH 3~5 of media.