It is disclosed an mounting bracket for air conditioner including a supporting bottom bracket and a mounting standing bracket; wherein the mounting standing bracket includes a standing bracket fixing portion and a standing bracket sliding portion which are slidably connected with each other to form a frame structure, and the supporting bottom bracket is hinged with the standing bracket fixing portion. The mounting bracket further includes a connecting rod which is a telescopic rod with one end thereof connecting to the standing bracket fixing portion and the other end thereof connecting to the supporting bottom bracket. The air conditioner is supported by the supporting bottom bracket and is fixed by the mounting standing bracket into the mounting bracket, and then the mounting bracket is fixed on the window to support and fix the air conditioner.