Ultra Trail Serra de São Mamede is a cross-border trail running series based in Portalegre, eastern Portugal, near Spain. Its longest race covers approximately 105 to 110 km with 5,000 to 5,500 metres of elevation gain, classifying it as mountain ultra running. Shorter distances are available, around 75 km, 50 km, 25 km, and 15 km, with a short trail or walk option in some editions. Atletismo Clube de Portalegre organizes the event, which is listed on the Portuguese National Trail Ultra Endurance calendar.
The routes traverse the Serra de São Mamede area and extend into municipalities such as Portalegre, Castelo de Vide, Marvão, and Valência de Alcântara in Spain. Much of the running takes place within the Serra de São Mamede Natural Park, with forest, mountain terrain, and border trails defining the race. Starts differ by distance, but the finish is consistently at UTSM Arena, the Municipal Stadium of Assentos. The event attracts hundreds of participants from multiple countries, awards ITRA points, and serves as a UTMB qualifying race, adding significance to the long course for experienced trail runners.