Abstract: In seasons of tapping Styrax trees (Styrax hypoglauca Perk.), it is found that benzoin yields will increase significantly if the bark of stem base was slightly scraped and treated with a 10% Oil preparation of ethrel at 10–12 days prior to balsam cutting. The average benzoin yield for treated trees has been found 8–17 times as much as those of the controls. There are many advantages for application of ethrel, such as, convenient to use, resulting in larger amplitude of productive increment, only a slight in jury to the bark, and no changing in benzoin composition, etc. Thus, ethrel may be applied unquestionably to the purpose of benzoin production. It is also proved that ethrel can enlarge the size, increase the total number and broaden the distribution ranges of traumatic balsamic ducts. And then, it increases the benzoin yields.