This paper reports a new method for fabrication of microlens arrays using a polyoxymethylene (POM) mold with concave-type cylindrical holes prepared by mechanical-micro milling without photolithography and wet etching processes. Microlens arrays were fabricated by a replica molding process using the concave-type POM mold. A polymethylmethacrylate (PMMA) thin film was deposited onto the POM mold and a concave PMMA template was prepared by blowing a nitrogen gas stream onto the thin PMMA film suspended on the micro POM mold. Microlens arrays were fabricated by pouring ultraviolet (UV)-epoxy onto the concave PMMA template and curing the UV-epoxy under UV light. Two types of microlens arrays, one with a hemispherical structure and one with a truncated-cone-type structure, were fabricated. After attaching the hemispherical microlens array onto organic light-emitting diodes (OLEDs), the external quantum efficiency (EQE) of the OLEDs was enhanced by approximately 56.5%. This work provides a valuable method for easy fabrication of microlens arrays with diameters of several hundred micrometers.