The purpose of this study is to explore the feasibility and superiority of using rapid expansion of supercritical solution (RESS) technology in the field of traditional Chinese medicine.  The extract of magnolia bark (EMB) was obtained by supercritical carbon dioxide (SCF-CO₂) extraction technology.  Microparticles of EMB were manufactured by RESS technology.  The effects of operating temperature and pressure on the   contents of the active ingredient in the particles were evaluated by HPLC.  The effect of expansion conditions on the particle size distribution of EMB particles was investigated.  The smallest sample (mean size: 4.7 μm) was obtained under the RESS condition: pressure of 25 MPa, temperature of 50 ℃ and a nozzle size of 100 μm.  The characteristics of microparticles were also studied by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and image analysis.  The dissolution rate study showed that microparticles had a   significantly faster dissolution rate than normal material particles.  After oral raw EMB suspension, the mean areas under the plasma concentration-time curves (AUC_0−t) of honokiol and magnolol were found to be (4.23 ± 0.36) and (5.46 ± 0.57) mg·h·L⁻¹, respectively, which were increased significantly, i.e. (5.41 ± 0.63) and (7.24 ± 0.83) mg·h·L⁻¹ when micronized EMB suspension was administered orally in SD rats (P < 0.05).  Similarly, the mean maximum plasma concentrations of honokiol and magnolol increased from (1.55 ± 0.22) and (2.35 ± 0.14) mg·L⁻¹ (raw EMB) to (2.31 ± 0.17) and (2.84 ± 0.21) mg·L⁻¹ (micronized EMB), respectively.  The results of t-test demonstrated that AUC_0−t and C_max value for honokiol and magnolol was significantly increased with the micronization compared to raw EBM (P < 0.05).  This study demonstrated that the RESS was applicable for preparing microparticles of EMB at low operating temperature.  The process was simple, free of environment pollution and without residual solvent.