Activation tagging is an important strategy in plant genomics by generating gain-of-function mutants. In this work, a library of Arabidopsis mutants was constructed by in planta transformation mediated by Agrobacterium tumefaciens containing an activation tagging vector pSKI015 with herbicide Basta as a selection marker (Fig. 1). Among 20000 independent transformants, 38 lines, i.e. about 0.2% of T(1) progeny, show visible morphological phenotypic variations (Fig. 2). Results of Southern blot analysis revealed that most of the transformants have more than three copies of T-DNA insertion (Fig. 3). Plasmid rescue and TAIL-PCR were used to recover the flanking genomic sequences of mutated target genes as the first step towards mutant gene cloning (Fig. 4, 5).