In this study, the effects of the thickness, fiber diameter, and solidity of rear acoustic absorbents on sound absorption coefficient were investigated. Polyester $100\%$ nonwovens (needlepunching) consisting of different fiber fineness were selected for rear acoustic absorbents. The capacity of sound absorption was measured by the two-micro-phone impedence measurement tube (KS F 2814), and sound absorption coefficient was calculated. Air permeability (ASTM D 737) was measured to estimate the structural characteristics of acoustic absorbents. It was found that the amount of sound absorption by rear acoustic absorbents increased throughout the whole frequency range with increasing thickness and solidity, and with decreasing fiber diameter, which results from the reduction of air permeability. Based on the results of this study, it is expected that efficient sound absorption capacity through the whole frequency range can be achieved by applying various combination of rear acoustic absorbents to the interior of buildings.