The binary vector pCAMBIA3300-gpdA-hph-trpC with hygromycin B phosphotransferase (hph) was constructed and transformed into Monascus albidus 9901 by Agrobacterium tumefaciens-mediated transformation, with gene hph as the selective marker. In order to improve the efficiency of A. tumefaciens-mediated transformation in M. albidus 9901, we optimized various factors including concentration of M. albidus 9901 spores, cell density of A. tumefaciens, co-cultivation time, temperature, and acetosyringone concentration. Most transformants of M. albidus 9901 could grow stably on media containing 50 mu g ml(-1) hygromycin B up to five generations. The presence of hph was identified by PCR. Two transformants H1 and H2 which produced more Monacolin K than M. albidus 9901 were screened, and the concentration of Monacolin K in the fermented millet by H1 and H2 increased by 42.15% and 40.34% respectively compared with that produced by M. albidus 9901.