An efficient transformation system employing Agrobacterium tumefaciens-mediated transformation was developed for the fungal biocontrol agent Beauveria bassiana. The system was successfully applied to integrate the hygromycin resistance gene and green fluorescent protein gene into B. bassiana with a transformation frequency of 13–22 transformants per 10⁶ conidia. The majority of transformants harboured a randomly integrated single copy of T-DNA that was mitotically stable. The described protocol could provide a useful tool in genetic manipulation of B. bassiana, while the green fluorescent protein mutants generated with this technique will be useful for the detailed study of B. bassiana infection and colonisation of a host organism.