Roads are one the most important human agents of transformation, producing direct non natural, negative effects in wildlife. This work quantified road mortality on amphibian and reptile species in the Hoces del Alto Ebro y Rudrón Natural Park (north of Spain). In 2005, two types of roads (seven secondary and one main road) were sampled by car in order to detect road-killed specimens. Geographical Information Systems (GIS) and G-tests were used for analysing data, and mortality indexes (MI, number of specimens / 100 km sampled) were used as descriptors of the mortality risk on wild species. A total of 291 specimens was recorded, 115 amphibians belonging to four species and 176 reptiles belonging to 13 species. Bufo bufo represented more than 88% of the amphibians with MI peaks in spring and autumn. Natrix maura, Vipera aspis and V. latastei were the most frequently found road-killed reptiles (54.5%), presenting the two viper species MI peaks in spring. The number of road-kills was significantly higher in secondary roads than in the main one and also significantly high in well-preserved habitats. Three sections of high mortality were identified, all located in secondary roads that go through the Natural Park, enhancing the importance of habitat fragmentation as a major threat in biodiversity conservation. Management actions to reduce and/or eliminate the intensity of road mortality should be addressed in the Natural Park's management plan and detailed studies should be performed to evaluate the effectiveness of installing traffic signs, road barriers and/or under-road passages.