p-Hydroxymandelic acid (4-Hydroxymandelic acid; 4-HMA) is widely used in production of aromatic drugs and flavors. It is employed for the preparation of 4-hydroxyphenylacetic acid, which is the synthetic precursor of selective β1-receptor antagonist drug atenolol. p-Hydroxymandelic acid can conjugate cytotoxic drug and enzyme substrate, and such a p-Hydroxymandelic acid based adaptor system showed promising application in the targeting drug delivery system.