Abstract: A locking mechanism for double-sliding sashes is provided to fasten inside and outside sashes and lock the fastened sashes to a window frame by a single operation using a handle. The mechanism comprises a crescent sash fastener composed of a fastening member and a receptacle member. The receptacle member is revolvable by being pushed by a projection of the fastening member which is revolved by a handle to fasten them together. The revolving movement of the receptacle member is converted into a vertical movement of a driving rod provided in a meeting stile of the outside sash. The vertical movement of the driving rod rotates locking levers which are linked to the rod at the upper and lower ends thereof to push the window frame in a firmly secured condition.