Three hundred and thirty nests of Southern Grey Shrike Lanius meridionalis were located during 1998–2010 in two highly fragmented Mediterranean agricultural areas of Spain (Olite in Northern and Toro in Western part of the country). Most nests (ca. 85%) were built in thorny shrubs (mainly Dog Rose Rosa sp. and Blackberry Rubus ulmifolius) and thornless shrubs (mainly Holm Oak Quercus rotundifolia and Kermes Oak Quercus coccifera). Based on a logistic regression, three factors had an influence on breeding success: study area, breeding phenology, and plant cover type. Location of the nest inside the shrub, as well as luminosity inside a shrub varied between studied shrub species, but did not significantly affect breeding success. The percentage of successful nests was significantly higher in Olite than in Toro (64.5% and 37.9% respectively). In Olite, but not in Toro, clutches laid early (first egg laid prior to 1st May) were more successful than clutches laid late. The highest breeding success was recorded in nests located in thorny shrubs and, especially, in those found in Blackberry bushes. Conservation of Blackberry shrubs appears to be an appropriate measure to increase breeding success of the Southern Grey Shrike.