An Agrobacterium-mediated method for producing transformed maize or rice, culturing an Agrobacterium-inoculated immature embryo with a coculture medium and a regeneration step for culturing the immature embryo with a regeneration medium either without callus growth or after callus growth culture to regenerate whole transformed maize or rice. The method further includes a transformation enhancement and the method does not include any selection step based on the properties of a nucleic acid to be introduced by Agrobacterium in any step from coculture to regeneration.