The present invention aims to provide a method for producing a trans-polyisoprenoid which can increase trans rubber production. The present invention is directed to a method for producing a trans-polyisoprenoid in vitro, which involves the use of a gene coding for a trans-prenyltransferase (tPT) family protein and further involves the use of rubber particles bound to a protein encoded by the gene, or a method for producing a trans-polyisoprenoid, which includes introducing into a plant a vector including a promoter having a promoter activity that drives laticifer-specific gene expression and a gene coding for a tPT family protein linked to the promoter to express a protein encoded by the gene specifically in laticifers.
