This paper reports, for the first time, a new method of fabricating a 45°-micro-reflector-ended polymer waveguide using one-step UV embossing technique. This technique allowed us to fabricate an array twelve channel multimode polymer waveguides equipped with a 45°-micro-reflector by using a one-step UV embossing technique. For the embossing we used a 45°-ended silicon waveguide mold. The silicon waveguides mold has a 45° slope prefabricated at the end of each waveguide structure. First, a 1um-thick-SiO2 layer is grown on the (100) silicon substrate. Then, the waveguide channel is patterned. The patterned waveguide channel is tilted at 45° from (100) silicon alignment base line to use the wet etching morphology which has 90° and 45° etched slopes when exposed to KOH and isopropanol saturated KOH solutions. After that, silicon substrate is wet etched with KOH solution to form the rectangular waveguide patterns. Another thin SiO2 layer is deposited again to protect the waveguide patterns and substrate. A thin line is then patterned on the top of the waveguide structure and a thin-line shaped silicon surface of the top of the waveguide structure is opened. Then, the opened silicon surface is wet etched in KOH saturated with isopropanol solution. The other area is protected by SiO2 layer. The etched shape has a V-shape and the angle from the bottom side is 45°. After SiO2 removal and cleaning, 45°-ended silicon waveguide mold is completed. With this mold, UV embossing is performed to form undercladding structure and 45° slope simultaneously. And a metal film is coated on the surface of the 45° slope. And then, core polymer is filled and cured by UV irradiation. This method can be applicable to waveguide structures of sizes ranging from multimode to single mode.