Recently, there has been an increasing interest in the extraction of essential oils. In this article, polystyrene (PS) nanofibrous membranes (NFM) produced by electrospinning were applied as the extraction medium to extract onion essential oil. The NFM exhibited good compactness and adsorption/desorption. About 2 L of onion juice was completely passed through 500 mg PS NFM round plates of 10 cm diameters, then NFM sheet was spin-dried 5 min at 4,500 rpm and eluted by 50 mL of 100% ethanol. The eluant was distilled at 55°C and an amber oily liquid was obtained. A total of 37 compounds were identified by gas chromatography–mass spectrometry from onion essential oil, and the most representative compounds were organosulfur-containing compounds. Furthermore, the antioxidant activities of the essential oil were investigated and the oil showed antioxidant activities in ABTS assay (0.67 mg/mL as IC50 value), DPPH test (IC50 value = 0.70 mg/mL), metal chelating assay (IC50 value of 0.54 mg/mL) and assay (0.95 mg/mL as IC50 value), and the reducing power of the oil was dose-dependent. This work firstly demonstrated the potential of NFM as extraction medium for the extraction of essential oils and the significance of relevant research work. Practical Applications Over the last decades, lots of research work has been done on the extraction processes of essential oil and possible industrial applications. Recently, electrospun nanofibers have the potential to serve as a good sorbent material for solid phase extraction. In this research, NFM produced by electrospinning were applied as the extraction medium to extract onion essential oil. The results of this study clearly showed that the extraction process of essential oil by NFM was feasible. Amber onion essential oil by PS NFM treatments was obtained and rich in organosulfur-containing compounds and possessed moderate antioxidant activity via antioxidant tests in vitro and has great potential for application as a natural antioxidant agent.