An Acoustic Window is comprised of a horizontal sliding window at the inner layer, and a side-hung window, which can be pushed to open, on one side of the outer layer, and a fixed glazing on the other side. The glazing of the sliding inner window serves as a “baffle” for screening off the noise passing through the opened outer window when it is slid behind the opened outer window. This baffle-type acoustic window is proved to reduce up to 8 dB(A) road traffic noise and is gaining popularity in residential developments of Hong Kong, particularly for those located in difficult sites in close proximity to heavily trafficked roads. This paper presents the experimental results from a study looking into the acoustical transmission loss of Acoustic Windows with respect to changes in window configuration and setting of line sources. Based on the experimental results, empirical models for noise reduction of Acoustic Windows are developed and investigated to assist quick design of Acoustic Windows for planning residential developments.