This work describes a novel transparent micro-needle array for photodynamic therapy (PDT) applications. This micro-needle array, with 250um in height and 35um in diameter, was placed onto skin and penetrated the cuticle yet not reaching the corium layer, so as to avoid pain and bleeding but achieve superior light transmission efficiency. For PDT applications, this design can significantly reduce the required incident power and therefore avoid additional damage to surrounding healthy tissue. Practical in-vivo test on human skin demonstrates the improved power transmission efficiency (PTE) of two types of needle arrays is 1.41 and 1.71 times better than the condition without using micro-needle array.