Wholly aromatic polyamide fibers cut to a length of 0.5 to 5 mm are dispersedly contained in an injection-moldable thermoplastic resin, and the resin is molded by ultrahigh-speed thin-wall injection molding so as to produce a loudspeaker diaphragm in which the wholly aromatic polyamide fibers are dispersed in a direction perpendicular to the resin flow direction, whereby the loudspeaker diaphragm is improved in internal loss.