The present invention relates to a method for introducing a substance into a plant. The method of the present invention comprises the steps of: obtaining an enzymatically treated and isolated fertilized egg cell by (1-i) isolating a fertilized egg cell from a plant tissue containing a fertilized egg cell, and then treating the fertilized egg cell with an enzyme solution containing a plant tissue-degrading enzyme under a low-titer condition, (1-ii) treating a plant tissue containing a fertilized egg cell with an enzyme solution containing a plant tissue-degrading enzyme under a low-titer condition, and then isolating the fertilized egg cell that has been enzymatically treated, (1-iii) treating a plant tissue containing a fertilized egg cell with an enzyme solution containing a plant tissue-degrading enzyme under a low-titer condition, and simultaneously isolating the fertilized egg cell that has been enzymatically treated, (1-iv) isolating an egg cell and a sperm cell from a plant to produce a fertilized egg by fusing the cells, and then treating the fertilized egg cell with an enzyme solution containing a plant tissue-degrading enzyme under a low-titer condition, or (1-v) treating a plant tissue containing an egg cell with an enzyme solution containing a plant tissue-degrading enzyme under a low-titer condition, and then isolating the egg cell that has been enzymatically treated, and further fusing the egg cell with an isolated sperm cell; and (2) introducing a substance selected from the group consisting of nucleic acids, proteins, and peptides into the resultant enzymatically treated and isolated fertilized egg cell.