In this paper, we combined photolithography, polydimethylsiloxane (PDMS) molding, and UV- forming techniques to fabricate micro-truncated cone arrays. The base angle of micro truncated cone arrays was adjusted by changing softbake parameters during photography of photoresist. The fill factor of micro-truncated cone arrays was altered by varying the spacing between two neighboring cones. In addition, the influences of base angle and fill factor of micro-truncated cone arrays on efficiency improvement and optical properties of a blue light organic light-emitting diode (OLED) were investigated. The optical properties include spectral shift, CIE coordinates, viewing-angle-dependent luminance. Experimental results showed, the efficiency of the OLED increased with increasing the fill factor, but decreased with the base angle of micro-truncated cone arrays. The efficiency of the OLED could be increased up to 42% by attaching the micro-truncated cone array having a fill factor and a base angle of 94% and 72⁰, respectively.