This study explores the use of UAV-based photogrammetry for measuring vertical displacements during static load testing of a prestressed reinforced concrete beam. The UAV captured overlapping images from distances of 4 m and 10 m during three load phases, and 3D coordinates of signalized targets were computed using photogrammetric methods. Displacements derived from UAV data were compared with high-precision LVDT sensor measurements. Results show that UAV measurements match reference values, with RMSE at millimetre level. Accuracy decreases with distance due to lower resolution and image geometry quality. Despite certain limitations—such as sensitivity to lighting and the need for stationary scenes—the method demonstrated good repeatability and robustness. UAV photogrammetry offers a non-contact, cost-effective alternative for displacement monitoring and shows strong potential for broader application in structural diagnostics.