A novel decanoate conversion layer (DCL) with improved hydrophobicity for the corrosion protection of Mg alloy is fabricated and tested. XRD, EDX and FTIR results suggest that DCL comprises (CH 3 (CH 2 ) 8 COO) 2 Mg and Mg(OH) 2 . The contact angle of DCL increases with increased cycling number and reaches ca. 120° at the 30th cycle. The corrosion protection of DCL is much better than that of a decanoate inhibition layer, and close to that of a chromate conversion layer. With increased thickness, improved compactness and hydrophobicity, the decanoate conversion is proven to be a green and effective way to protect Mg alloys from corrosion.