An object of the present invention is to provide a method for efficiently producing polyploids in para rubber trees that are extremely useful for breeding new varieties. The method of the present invention is characterized by carrying out colchicine treatment on para rubber tree (Hevea brasiliensis) seeds after rooting. In the present invention, the seeds are preferably seeds that have rooted but have not yet germinated. In addition, colchicine treatment is preferably carried out by allowing the seeds to contact a colchicine solution having a colchicine concentration of 400 ppm to 800 ppm.
