Maize transposable element Ac was transformed into Brassica napus L. Westar via Agrobacterium tumefaciens in order to study the activity of Ac element and related mutagenesis. The segregation ratio of the report gene NPTⅡ deferred from Ac element in T 1progeny. Ac transposition activity was found in transgenic B.napus L. The index of sclerotinia stem rot decreased in groups with the increase of the Ac positive percentage. A liner relationship was found between ID and Ac positive percen...