A new chitosan ester derivative, chitosan p-hydroxybenzoate is synthesized, which is expected to have antimicrobial activity similar to parabens. The amino group of chitosan reacts well with acyl chloride to prepare a N-amic acid-chitosan. The amino group of chitosan must be protected before synthesizing a 6-O-chitosan ester. Phthalic anhydride is selected to react with chitosan to form N-phthalimide chitosan whose free amino group is protected. By six steps chitosan p-hydroxybenzoate is synthesized. FTIR, 1H NMR and 13C NMR spectra show that the ester bond is formed between p-hydroxybenzonic acid and chitosan. Water solubility of the ester is slightly better than that of heptyl p-hydroxybenzoate, and its solubility in alcohol is greatly improved. Chitosan p-hydroxybenzoate showes broader spectrum antimicrobial activities. It has strong antimicrobial effects against Gram-negative, Gram-positive bacteria and yeasts. The MICs of chitosan p-hydroxybenzoate for Staphylococcus aureus and Escherchia coli are 0.01% and 0.025%, respectively.