The aim of the study was to analyse the effect of physical properties of natural fibre to the sound absorption coefficient. It was also aimed to study the relation of the physical properties of natural fibre to wider the frequency range and increase the sound absorption coefficient. There were two types of natural fibre will be studied such as kenaf fibre and rice straw fibre. The performance of sound absorption coefficient was measured using fabricated impedance tube according to ISO 10534-2. The physical properties of the natural fibre may affect the sound absorption coefficient either shifted to low frequency or shifted to high frequency range. All the physical properties that influence the sound absorption coefficient of natural fibre will be explained. The physical properties of natural fibre that will be studied were fibre thickness, fibre diameter and compressed fibre. Results have shown that the fibre thickness and diameter have a big effect to sound absorption coefficient. From the results, the utilization of the sound absorption coefficient can be achieved by choosing the suitable natural fibre according to its physical properties for a suitable application.