To improve the transformation efficiency of plants, e.g. nice, corn and the like, and to obtain transformed plants having excellent herbicide- resistant property, pest-resistant property, cold-resistant property or drying- resistant property by cultivating plant tissues inoculated with Agrobacterium bacteria under a specific condition.

The transformed plant is obtained by cultivating plant tissues of corn (premature embryo) or the like inoculated with Agrobacterium bacteria in a culture medium containing a substance (the concentration is preferably 10 μM), e.g. silver nitrate, silver thiosulfate complex salt or the like, which inhibits the effect of ethylene or a substance (the concentration is preferably 0.5-1 μm), e.g. an ACC synthase inhibitor such as aminoethoxyvinyl glycine or the like, which inhibits the biosynthesis of ethylene. Further, transformed cells are preferably prepared by cultivating them in a medium containing carbenicillin (the concentration is preferably 100-250 mg/l).