This paper presents a development process of an advertising accessory including a light guide to be applied to mobile devices. At first, this research is to design an optical part as a light guide to transmit the light more than 10% of the LED light from mobile devices. Secondly, it presents the mechanical design of the part to be applicable to size changes of mobile devices and to enduring external forces. By using ANSYS and OPTISWORKS, a preliminary design including to tune the applied material properties is performed to prevent from the failure of the component, to maintain the proper pressure for holding mobile devices with different thickness, and to obtain enough optical transmission efficiency. In addition, this paper introduces a manufacturing process for the advertising accessory with a chemical and mechanical polishing. In order to measure the performance of the manufactured accessory, here, measurement devices such as measuring the pressing force, luminance, and illuminance are also designed and fabricated. Several modifications are made for the purpose of improving the measured performance.