A method of transforming a monocotyledon by means of agrobacterium. There is provided a method of transforming a monocotyledon by means of agrobacterium containing a desired recombinant gene. This transforming method comprises the steps of sowing a culture medium containing a plant growth factor with a monocotyledonous seed, conducting culturing for 1 to 3 days so as to effect germination and infecting the seed with agrobacterium. This method makes it feasible to rapidly transform monocotyledons, including a rice plant.