This study proposes a novel ultra-thin aluminum flat heat pipe with thickness of 1.5 mm for the first time in order to satisfy the ever increasing requirements for cost-effective, physically compact and highly efficient thermal management solutions. The extruded aluminum tube contains multiple separate micro cavities that work as independent micro heat pipes and a two-level compressing process is applied to flatten the tube to the ideal thickness. Sintered aluminum fibers and aluminum fiber meshes with surface treatment are inserted into each cavity of the ultra-thin heat pipe as the extra wicks for comparison. The thermal response characteristics of the fabricated aluminum heat pipes, including the temperature uniformity, thermal resistance, and effects of wick structure and inclination angles, are fully investigated. Under large inclination angle (90 degrees), the smooth heat pipe without any extra wick performs lower temperature difference, lower thermal resistance, and higher heat transport capacity compared to that with aluminum fiber wick whereas the heat pipes with wicks present superiority under smaller inclination angles (60 degrees and 30 degrees) due to the liquid backfiow enhancement. Besides, comparative study also shows that wick structure optimization holds the potential to improve the thermal performance of this ultra-thin two-phase device. (C) 2018 Elsevier Ltd. All rights reserved.