An adjustable brace for supporting a window air conditioner that includes: a pair of interior brackets on the inside adjustably attached to a pair of exterior brackets and a pair of locating brackets on the outside. The pair of interior brackets includes an interior leg extending downwardly from one end and adjustably secured to the wall by interior mounting plates. The pair of exterior brackets includes an exterior leg extending downwardly from one end and adjustably secured to the wall by exterior mounting plates. A cross member adjustably connects the two interior brackets to fit different size air conditioners. The adjustable brace extends through the window to adjustably support the window air conditioner.