The present investigation was designed to prepare chitosan microspheres and evaluate the in vitro release pattern of the drug isoniazid.The microspheres were formulated by glutaraldehyde cross-linking method using various concentrations of chitosan. The prepared microspheres were evaluated for drug content, particle size distribution, stability studies and compared with marketed tablets. The percentage of entrapment obtained was 60%. In vitro release studies were carried out in 0.1 N HCI and 88.1, 83.8, 79.3 and 73.0% of drug was released from 0.5, 1.0, 1.5 and 2.0% of chitosan microspheres respectively after 8 h. Stability studies were carried out at different temperatures and found that all the formulations were more stable at 4° and room temperature. © 2010 Elsevier B.V., All rights reserved.