Various preservation methods at low temperature have been reported for several powdery mildew fungi, but the conidia of Podosphaera aphanis causing powdery mildew of strawberry could not be preserved either at low temperature or by freeze-drying and liquid-drying of conidial suspensions or diseased leaf discs. Here, we developed a new technique for a labor-saving preservation of the conidia of the fungus by using the aseptic seedling culture of strawberry. Conidia produced on the seedlings could be preserved at 5°C for six months. Using this method, we could obtain the stable stock cultures of 12 strains collected from various regions in Japan.