The present invention provides a method for producing a polyisoprenoid with which it is possible to enhance the rubber synthesis activity of rubber particles to increase natural rubber production. The present invention relates to a method for producing a polyisoprenoid in vitro, which involves the use of a gene coding for a cis-prenyltransferase (CPT) family protein and a gene coding for a Nogo-B receptor (NgBR) family protein, and further involves the use of rubber particles bound to proteins encoded by these genes; or a method for producing a polyisoprenoid, which includes introducing into a plant a vector in which a promoter having a promoter activity that drives laticifer-specific gene expression is linked to a gene coding for a CPT family protein and a gene coding for a NgBR family protein, to express proteins encoded by the genes specifically in laticifers.