The chemical composition of the essential oil extracted from the aerial parts of Bubonium imbricatum, an endemic plant of southern Morocco, was analysed. GC-MS showed 51 compounds, representing 60.2% of the total oil. Thymol isobutyrate (18.3%) and 2,5-dimethoxy-p-cymene (16.2%) were the major constituents of the oil. The oil was tested for antifungal activity in mycelial growth inhibition tests in vitro against three agricultural pathogenic fungi: Penicillium digitatum, P. expansum and Botrytis cinerea. The oil at 1000 ppm was highly effective against mycelial growth of P. digitatum with 99% inhibition. For P. expansum and B. cinerea the percentage of mycelial growth inhibition at 1000 ppm was respectively 87.2% and 87.8%. At 2000 ppm the oil was 100% effective in controlling mycelial growth of all three fungi. B. imbricatum essential oil was also tested at different concentrations on citrus fruits (Citrus reticulata Blanco cv. Nules) inoculated with P. digitatum (105 conidia ml-1). The oil had a fungistatic or fungicidal effect on C. reticulata.