This paper reports a microlens array (MLA) film with full fill factor and presents its application to organic light emitting diode (OLED) for improving outcoupling efficiency. Gapless MLA film having high sag ratio is proposed and fabricated by simple micromachining process including trench formation and conformal vapor phase deposition of polymer. As applying MLA film to OLED panel, the outcoupling efficiency increased by maximum 48%. High-sag MLA optical film with full fill factor is expected to give remarkable optical efficiency to various display or lighting applications of the flat panel light sources including OLED.