The invention relates to a method for transforming a monocotyledonous plant. The time required from transformation to regeneration of a plant is shorter using the inventive method so that the frequency of emergence of mutants is smaller than the conventional methods. The inventive method may be generally applied even to the plants for which a regeneration method from a protoplast to a plant has not been established, and with which the preparation of the material to be subjected to the method is easy. That is, the present invention provides a method for transforming a monocotyledonous plant, comprising contacting a cultured tissue of said monocotyledonous plant during dedifferentiation thereof obtained by culturing an explant on a dedifferentiation-inducing medium for less than 7 days with a bacterium belonging to the genus Agrobacterium containing a super binary vector having the virulence region of a Ti plasmid, left and right border sequences of T-DNA of a Ti plasmid or an Ri plasmid of a bacterium belonging to the genus Agrobacterium, and a desired gene located between said left and right border sequences.