6-Oligo(lactic acid)cyclomaltoheptaose (6-OLA-betaCD) with an average substitution of about 7.0 lactic acid units was prepared as a new water-soluble cyclomaltoheptaose (betaCD) derivative (solubility of about 70.7-fold that of betaCD), based on the ring-opening polymerization of 3,6-dimethyl-1,4-dioxane-2,5-dione (lactide). The product was characterized by (1)H NMR, (13)C NMR, IR, and MS spectroscopy. The complexation of amoxicillin with 6-OLA-betaCD was found to be much stronger than that with betaCD at first, and then 6-OLA-betaCD was shown to decompose moderately into betaCD and lactic acid. 6-OLA-betaCD might be greatly valuable in a controlled release system for Amoxicillin (AMX).