Oak decline in non calcareus soils in south-western Spain has been associated with Phytophthora cinnamomi for decades. However, other Phytophthora species such as P. quercina and P. psychrophila have been associated with Quercus decline in the eastern part of Spain where calcareous soils are predominant. With the aim of investigating the involvement of Phytophthora spp. in oak decline in eastern Spain, two forests in different geographical areas were selected as sampling sites: the Natural Park ‘Carrascar de la Font Roja’ (Alicante) and the Natural Park ‘Tinença de Benifassà’ (Castellón). Soil samples were analyzed in parallel by isolation using baiting methods and by amplicon massive sequencing.