Biodegradable microspheres were prepared with poly(L-lactide-co-glycolide)(PLGA, 75:25 by mole ratio) by an oil/oil solvent evaporation method for the sustained release of anti-AIDS virus agent, AZT. The microspheres of relatively narrow size distribution (7.6 ± 3.8 ㎛) were obtained by controlling the fabrication conditions. The shape of microspheres prepared was smooth and spherical. The efficiency of AZT loading into the PLGA microsphere was over 93% compared to that below 15% for microspheres by a conventional water/oil/water method. The effects of preparation conditions on the morphology and in vitro AZT release pattern were investigated. In vitro release studies showed that different release pattern and release rates could by achieved by simply modifying factors in the fabrication conditions such as the type and amount of surfactant, initial amount of loaded drug, the temperature of solvent evaporation, and so on. PLGA microsphers prepared by 5% of initial drug loading. 1.0% (w/w) of surfactant concentration, and 25℃ of solvent evaporation temperature were free from initial burst effect and a near-zero order sustained release was observed. Possible mechanisms of the near-zero order sustained release for our system have been proposed.