Pinus merkusii shows great potential as a resin-producing wood in Indonesia, with the global demand for pine resin reaching 1 million tons annually. This study investigated the effect of ethephon on the anatomical properties of P. merkusii, particularly the resin duct that affects resin productivity, to increase the efficiency of pine resin tapping. Ethephon was mixed with Vaseline to create concentrations of 0%, 2%, 4%, and 8% and then applied to the seedlings at 0.5 g for 3 and 6 weeks. The re