PROBLEM TO BE SOLVED: To provide a method of efficiently producing polyploid plant cell and hybridized plant by artificially fusing ootid and spermatid obtained from plants.SOLUTION: There is provided a producing method for polyploid plant cell comprising: (a) a step of producing fertilized cell by fusing spermatid and ootid； and (b) a step of fusing one or more cells selected from a group consisting of fused cells in which ootid and ootid are fused with the fertilized cell. There is provided a method of producing polyploid of plant comprising a step of differentiating polyploid plant cell produced by the method. There is provided a method in which the fused cell in which ootid to be fused with the fertilized cell or fused cell in which ootids are fused is homogenous to the species of the spermatid； or the spermatid and ootid to be integrated in step (a) are derived from the same species and the ootid fused with the fertilized cell in step (b) or one or more of fused cells in which ootids are fused is derived from different species from the spermatid.SELECTED DRAWING: None
