Novel water-soluble derivatives of silybin of enhanced activity are provided as well as methods of preparing the derivatives and pharmaceutical compositions containing them. The novel derivatives according to the invention have the following general formula (I); ##STR1## where: R=H or PO(OH).sub.2 and R'=PO(OH).sub.2 The compounds of the invention are useful inter alia in therapy of liver disorders and other applications where an anti-radical effect is required. They have the advantages of high hydrophilicity and are soluble at approximately pH 4, compared to prior art compounds which are water-soluble only at higher pH and enhanced stability.