Alzheimer's disease is a neurodegenerative condition that affects approximately 5 million people and is the fourth leading cause of death in America. Tacrine is one of the three drugs approved by the FDA for the treatment of Alzheimer's disease. However, the drug has a short biologic half-life of 2-3 hr and gastrointestinal, cholinergic, and hepatic adverse reactions that are associated with high doses of the drug. The aim of our study was to formulate a controlled release delivery system of tacrine that could be used to minimize the side effects associated with the drug. Microparticles of tacrine were formulated using poly(D,L-lactide-co-glycolide) (PLG). PLG and tacrine were dissolved in mixed organic solvents and added to a polyvinyl alcohol solution that was stirred at a constant rate. The organic solvent was evaporated overnight and the formed microparticles were collected by filtration, dried, and sieve-sized. The effects of such formulation variables, as molecular weight of polymer, stir speed during preparation, and drug loading on encapsulation efficiency (EEF), and in vitro release profiles of tacrine were investigated. An increase in the molecular weight of polymer from 8,000 to 59,000 and 155,000 resulted in approximately 10-fold increase in EEF, but the rate of release decreased with increasing molecular weight. Stir speed during preparation had an effect on the EEF but not on the rate of release. Drug loading did not have a significant effect on the EEF but had an effect on the rate of tacrine release. The results suggest that tacrine could be delivered at controlled levels for weeks for the treatment of Alzheimer's disease.