Synthetic foams are widely used as sound insulator and noise control application. Acoustic propertiesof this materials are affected by the chemical composition of polymer, microstructure parameters, morphological properties and processing conditions. In this research , the microcellular LDPE foam were produced using various amount of 0.5 , 2 , 3.5 and 5 phr Nano CaCO 3 as nucleating agent at 140, 160 and 180 °C for foaming process by the compression moulding method. Images from samples were obtained from Scanning Electrom Microscopy (SEM) and cell sizes were characterized by Image J software. Cell size distribution of foams were calculated by statistical analysis and the suitable distribution function for describing cell size distributio were determined by curve fitting method. Sound absorption coefficient of foams were measured and relationship between cell size distribution and sound absorption coefficient were investigated. Results show that the sound absorption coefficient of samples with rodbard cell size distribution function are higher than samples with other cell size distribution function. Keywords: Microcellular LDPE foam, Acoustic, Sound absorption, Cell size distribution