The invention refers to an isolated extract of walnuts of high efficiency and stability over time useful for the manufacture of a medicament for the treatment of viral, fungal and bacterial diseases, which is characterized in that it is obtained from a process comprising: i) collecting unripe walnut fruits as raw material； ii) preparing the raw material for the extraction, iii) freezing the raw material prepared in the previous step； iv) drying； v) extracting in a time lower than 10 minutes； vi) filtration； and vii) final packaging. The invention also refers to its use for manufacturing a medicament for the treatment of bacterial, fungal and viral diseases and to a composition comprising it.
