Supercritical fluid extraction (SFE) of the monoamine oxidase (MAO) inhibitor from antler velvet with CO2 was explored. The effect of different parameters, such as particle size, the kind of co-solvent, extraction temperature and pressure, on the extraction yield (Y) and the total inhibitory activity (TI) on MAO-B were investigated using three-level orthogonal array design. The experimental results show that when the absolute ethanol as co-solvent was used and the particle size was 120 mu m, the extraction temperature was 70 degrees C, the extraction pressure was 30 MPa, the extract yield reached 3.58% and the TI of the extract was 3319.13 U/g. Evaluation of the inhibitory activity of extract on MAO indicated that the extracts had strong inhibitory effects on MAO-B, but had slight effects on MAO-A. The MAO-B activity was inhibited by 93.77% at the concentration of 278.15 mg/L. which was much higher than that of water extract and ethanol extracts. The compositions of estradiol, uracil, hypoxanthine, p-hydroxybenzaldehyde and phospholipids in the SFE extracts were identified, which were reported to have the inhibitory effect on MAO. (c) 2008 Elsevier B.V. All rights reserved.