The absorption of lower-frequency when the incident wavelength is larger sound is problematic with fibrous material made up of coarser fibers. In that case, highly efficient sound absorption materials from much finer fibers must be developed. Electrospun nanofibrous membranes are also a novel subject to analyze their acoustic characteristic although studies on acoustic properties of conventional textile materials started in nineties. Nanofibrous membranes can improve acoustic insulation products by increasing the sound absorption coefficient, reducing material thickness, and decreasing material weight offering a competitive advantage. The purpose of this study is to analyze the effect of fiber diameter on acoustic behavior of nanofibrous membranes.