In 2002, the occurrence of fungi of the order Erysiphales on plants of the Słowiański Park located in Goorzów Wielkopolski was investigated. Plant samples were collected once a month, from August to November. The samples examined were above ground plant parts colonized by powdery mildew fungi. A total of 78 samples were collected. Apart from 14 species of the order Erysiphales, <i>Ampelomyces quisqualis</i> parasitizing on <i>Erysiphe cichoracearum</i> var. <i>cichoracearum, Phyllactinia mali</i> and <i>Podosphaera tridactyl</i> var. <i>tridactyla</i> was found. <i>Ampelomyces quisqualis</i> affected hyphae, oidia, and young cleistothecia of <i>P. mali</i>. In contrast, in <i>E. cichoracearum</i> var. <i>cichoracearum, Po. tridactyle</i> var. <i>tridactyla</i>, this hyperparasite colonized only hyphae and oidia. This paper for the first trime informs of <i>A. quisqualis</i> parasitizing on <i>P. mali</i> and <i>Po. tridactyla</i> var. <i>tridactyla</i>.