Solid oxide fuel cells (SOFCs) are promising electrochemical devices that directly convert chemical energy into electrical energy with high efficiency, fuel flexibility, and environmental compatibility. To enhance its commercial viability, recent research has focused on developing intermediate-temperature SOFCs (IT-SOFCs, 500-700°C), which mitigate issues related to material degradation and thermal cycling in high-temperature systems. However, lowering the operating temperature inevitably reduces ionic and electronic conductivity, leading to degraded electrochemical performance. To address this, thin-film SOFCs (TF-SOFCs) employing a dense and thin electrolyte supported by a porous anode have emerged as an effective structure to maintain high power output at reduced temperatures. A major challenge in fabricating TF-SOFCs lies in the limitations of conventional anode supports. Anode supports fabricated via conventional powder-based sintering methods often exhibit rough surfaces and large pores making it difficult to deposit thin and dense electrolyte without defects. To overcome this issue, an anode functional layer (AFL) commonly added between the anode and electrolyte is introduced. This layer smooths the surface and improves compatibility with the electrolyte. Specifically, nanostructured AFLs (n-AFLs) with fine grains increase the triple-phase boundary (TPB) and promote charge transfer leading to the enhanced electrochemical performance. Despite these advantages, the practical implementation of n-AFLs remains hindered by limited scalability and process complexity when fabricating the layer with thickness exceeding 1 μm. In this context, vacuum-based deposition methods, such as reactive magnetron sputtering, offer significant potential due to their controllability, uniformity over large areas, and compatibility with multi-layer fabrication. Reactive sputtering allows for co-deposition of composited oxides by introducing reactive gases such as oxygen, during the sputtering process thereby enabling precise tuning of film composition and microstructure. In this study, we report the scalable fabrication of nanostructured AFLs using reactive magnetron sputtering for high-performance TF-SOFCs. A large-area (5 x 5 cm 2 ) n-AFL was deposited onto porous anode substrate, followed by 1200°C annealing to ensure densification and mechanical stability. Through the optimization of sputtering power and oxygen partial pressure, we successfully suppressed the formation of thermally induced pores, cracks, and Ni agglomeration. The resulting n-AFL exhibited a dense yet nanoscale morphology with improved electrochemical activity. The optimized n-AFL implemented TF-SOFCs achieved a peak power density of 1.33 W/cm 2 at 650°C, highlighting the effectiveness of the microstructural control through reactive sputtering. Furthermore, large-area TF-SOFCs with an active cell area of 4 x 4 cm 2 were fabricated to demonstrate the scalability of the development. The cell with the optimized condition exhibited a total output of 19.36 W at 650°C. This value, to the best of our knowledge, represents the highest electrochemical performance reported for TF-SOFCs fabricated with reactive magnetron sputtering. This work demonstrates a scalable and effective approach to fabricate n-AFL via reactive sputtering. It provides a practical route toward large-area, intermediate-temperature SOFCs with high power output.