6"-O-Acetylginsenoside Rb-1 (ac-Rb-1) isolated from North American ginseng was encapsulated within biodegradable poly(DL-lactide-co-glycolide) (PLGA) microspheres. Both a conventional double emulsion and a microfluidic technique were examined for microsphere formation. The ac-Rb-1 encapsulation within PLGA microspheres was characterized by various physicochemical techniques including FTIR, DSC, and XRD. The experimental data showed that the PLGA microspheres produced from the microfluidic technique were uniform with tunable mean diameters from 7 to 59 mu m and standard deviations less than 10%. The size was independent of the capillary number and could be tuned by altering the continuous and disperse phase flow rate ratios. Release profiles from the uniform microspheres were investigated, showing controlled release of ac-Rb-1 which followed a Fickian diffusion while retaining potency toward immunosuppressive activity using macrophages in vitro. This study shows that ac-Rb-1 encapsulated PLGA microspheres obtained using the microfluidic approach are promising for the development of next-generation biomedical agents.