The promotion of taxol formation by Cu²⁺ is descri bed in this pa per. The optimum improvement of taxol production by Cu²⁺ was got when 30 μmol／L CuCl₂ cell suspension cultures was added on the 20th day after inocu lation, namely, the end of exponential growth phase. The cell growth was not significantly affected by the adding, but the intracellular soluble protein con tent and phenylalanine amonia-lyase activity of cell suspension cultures, and t he medium pH value changed.