Abstract: A one-step synthesis of oxo-crown ethers by ring-enlargement of γ-butyrolactone with propylene oxide catalyzed by Mg-Al composite was investigated. The formation of oxo-crown ether structure in the above reaction was identified by FT-IR，HPLC-(ESI)MS and UV. The novel synthesis route was simple and convenient，and had the advantage of high conversion of γ-butyrolactone without using any diluent. The experimental result showed that conversion of γ-butyrolactone reached 90.4% at 150—160 ℃ and 0.5—0.6 MPa when the mole ratio of PO to GBL was 13∶1.