Supercritical fluid (SCF) encapsulation technology is a frontier, green and innovative process that is gaining interest for polymeric formulation of drugs and other bioactives. In this study, pharmaceutically approved biodegradable polymers, polyethylene glycol (PEG ~4000 g/mol) and polycaprolatone (PCL ~10000 g/mol) were processed in supercritical carbon dioxide using particles from gas-saturated solutions (PGSS) technique. The PGSS particles were co-precipitated and micronized with Eucalyptus essential oil through a 500 µm nozzle. The effects of process time, reactor temperature and pressure, weight ratios of PEG/PCL and oil/polymer on encapsulation efficiency, loading capacity, release rate and radical scavenging activity were investigated and optimized using Taguchi L8 orthogonal array design. Incorporation of the eucalyptol-rich oil in the PGSS co-precipitated particles was confirmed by FTIR, UV-VIS spectroscopy and GC/MS. Statistical analysis of the selected response indices showed that encapsulation and release characteristics of the oil could be significantly controlled by modulating the limiting process conditions and formulation parameters under their optimum levels. SEM and GC/MS analyses of the optimized PGSS particles predicted by the Taguchi approach revealed broad size distribution of microparticles (50 – 300 µm) and slight alteration in the chemical composition of the microencapsulated oil. Release of the essential oil in simulated fluids from the polymeric microparticles was sustained over a period of 24 hours and the time-course radical scavenging activity of the PGSS particles strongly correlated to the release efficiency (r2 = 0.9). Conclusively, optimized bioactive formulation of polymer-oil microparticles with high encapsulation efficiency and sustained release profiles was produced using supercritical carbon dioxide.