Synthesis and biological evaluation of novel taxol derivatives having a phosphonoxyphenylpropionate ester group at the 2'-position or at the 7-position of taxol are described. These were found to have much improved water solubility and both were found to generate taxol upon exposure to alkaline phosphatase. A particular derivative, 7-phosphonoxyphenylpropionate of taxol 3b exhibited antitumor activity comparable to that of taxol against the ip/ip M109 murine tumor model.