Abstract: To investigate the role of MLO gene in powdery mildew resistance in Rosaceae, virus-induced gene silencing (VIGS) was used to inhibit the expression of RgMLO6 gene in Rose odorata var. gigantea and RlMLO7 gene in Rose longicuspis var. longicuspis. Then mildew was inoculated to identify the resistance of these two genes. The results showed that the relative expression levels of RgMLO6 and RlMLO7 genes in silenced plants decreased by 80%−90% after 20 days of VIGS vector transformation. The powdery mildew resistance of the young leaves silenced by the two genes was identified, and the resistance levels of Rosa odorata var. gigantea and Rosa longicuspis var. longicuspis were improved compared with the control group. The growth of mycelium in leaves of powdery miltiorrhiza after inoculated with two genes was observed under microscope. The growth of powdery mildew on leaf epidermis cells of silent plants was slower than that of control group. The results showed that RgMLO6 and RlMLO7 genes had negative regulation on powdery mildew in Rosaceae.