Microencapsulation of nalidixic acid using Eudragit RL, a methacrylic acid copolymer was investigated. Microcapsules were prepared by dispersing the drug solution in liquid paraffing using aluminium tristearate as dispersing agent. The preparation of the microcapsules showed high reprodulibility in particle size, shape and the drug content. The dissolution rates of Nalidixic acid from the these microcapsules considerably decreased as compared with that from Nalidixic acid powder and Nalidixic acid-Eudragit RL solid dispersions. The release of Nalidixic acid increased with increasing percentage of aluminium tristearate added to the microcapsules.