Abstract: A smaller-sized and acoustically excellent speaker diaphragm is inexpensively provided using the mixture of a specially surface-coated woody material and a mass-producible synthetic resin. The mixture is composed of a non-chlorinated synthetic resin and a powdery cellulose material whose particle size falls within a range of from 5 ?m to 500 ?m. The cellulose material has been subjected to a surface treatment to enhance its affinity to the non-chlorinated synthetic resin, and 30% to 70% by weight of the cellulose material is contained in the mixture.