Aims <p>The olive tree is a major crop in Mediterranean countries, but its cultivation faces growing challenges due to climate change. Nematophagous fungi are considered key components of soil ecosystems and can potentially control plant-parasitic nematode populations. This study aims to explore the diversity of these fungi in Mediterranean olive groves, assess their potential for controlling plant-parasitic nematodes, and identify the factors that influence this activity.</p> Study design <p>Forty-two olive groves across four countries (Greece, Morocco, Portugal and Spain) and two management practices (organic and non-organic) were sampled.</p> Methodology <p>The diversity and activity of nematophagous fungi were assessed using two approaches. First, nematodes community DNA extracted from 500 cm³ of soil was analysed via qPCR to quantify six target fungi actively attacking the nematodes population. Second, an egg-bait in vitro bioassay was used to detect the broader presence of nematophagous fungi at each site.</p> Results <p>Important differences in nematophagous fungi diversity and activity were found among countries, but not by olive grove management. Greece had the most diverse and active nematophagous fungi. Fungal ovicidal activity was significantly related to climatic conditions, as aridity increased, the infection rate decreased. According to the qPCR results, <i>Purpureocillium lilacinum</i> was the most prevalent and was detected in all countries. <i>Drechslerella dactyloides, Orbilia oligospora</i> and <i>Hirsutella rhossiliensis</i> had low prevalence. <i>Catenaria</i> sp. and <i>Gamsylella gephyropaga</i> were not detected.</p> Conclusion <p>Organic management does not necessarily increase the presence and diversity of nematophagous fungi in olive Mediterranean groves which appear primarily influenced by climatic and edaphic conditions.</p>