Juglans neotropica Diels, also known as "Nogal" or "Tocte," member of the Juglandaceae family is a tree native to the South American Andes with its natural habitat spanning Ecuador, Colombia, Peru, and Bolivia. Regarding its fruit, the walnut of Nogal is covered by yellow flesh. The walnuts are susceptible to invasion by various fungi both in the field and during storage, resulting in potential mycotoxin production. The main objectives of this study were to determine the fungi found in immature J. neotropica walnuts through their morphological structure, determine the possible fungal mycotoxins present and describe approaches to minimize the presence of fungi and mycotoxins in the walnut industry supply chain. Asymptomatic, and symptomatic green fruits were collected from 12 walnut trees located in the city of Quito, province of Pichincha, Ecuador during the fourth week of January 2024, which according to the analysis they were between 50% and 60% of the final sizeAfter sterilization and appropriate incubation, mycelia from the fungal colonies that grew were transferred to fresh potato dextrose agar (PDA). Macroscopic and microscopic morphology was described. The results were that 60% of the samples belonged to Alternaria genus, 8% belonged to Penicillium genus and 32% remained unidentified. According to the Alternaria genus the possible mycotoxins present in walnuts could be alternariol (AOH), alternariol monomethyl ether (AME), tenuazonic acid (TeA), altenuene (ALT) and altertoxins (ATX-I, -II, -III). According to the Penicillium genus the possible mycotoxins present in walnuts could be patulin, penicillic acid, citrinin, citreoviridin, cyclopiazonic acid, roquefortine C and especially ochratoxin A. The main approaches to minimize the fungi and mycotoxin contamination in walnuts are preventive measurements with adequate agronomic practices, controlling parasitic insects or other biotic stressors in order to prevent lesions in the walnuts, storage requirements control based on the oil and fatty acid compositions and establish a HACCP strategy encompassing all stages of the supply chain.