Abstract: By the reaction of chitosan with vanillin,Schiff's base was firstly obtained,followed by the eaction of NaBH₄ with Schiff's base to yield water-soluble N-(4-hydroxy-3-mehtoxybenzyl) chitosan (VCS).The chemical structure of the modified chitosan VCS was characterized by FTIR,¹H NMR and UV spectroscopies.Degree of substitution of N-4-hydroxy-3-mehtoxybenzyl determined with colloid titration was 2.37 mmol/g.The swelling characteristics of hydrogels(VCSG) prepared by cross-linking of glutaraldehyde with VCS were studied.The results showed that the swelling ratio(SR) of VCSG was decreased with the increasing of the dosage of glutaraldehyde.The swelling ratios of VCSG with different cross-linking degrees were decreased with the increasing of the pH value of the buffer solution between 1.2 to 7.4.The swelling ratios of VCSG were increased with the increasing of the pH value of the buffer solution between 9.0 to 11.0.The VCSG with a lower cross-linking degree swelled more significantly in a pH=1.2 buffer solution than in other medium,the VCSG with a high cross-linking degree swelled similarly and lower SR in buffer solution with different pH values.VCSG showed pH-sensitive in buffer solutions.The release behavior of famotidine entrapped in the hydrogel showed different speeds with the change of the pH value of medium in vitro.The release speeds of famotidine in VCSG in the media of pH=1.2 and 3.0 were much faster than those in the media of pH=5.0 and 7.4,both showed slow release effect.VCSG is pH sensitive and the swelling behavior of VCSG can be regulated by changing the dosage of the cross-linking agent,and has the potential as being the carrier for controlling drug release.