This study aimed to analyze the phytochemical profile and drying with prediction of the leaves of Ocimum citriodurum L, quantify the total phenolics and flavonoids and determine the unprecedented potential of the fungicidal activity of the oil-in-water nanoemulsion incorporated with essential oil and hydroalcoholic extract of O. citriodurum L. The leaves were carefully selected in the rural area of São Luís, Maranhão, Brazil, and subsequently crushed and stored. The essential oil was obtained by hydrodistillation (100°C / 3h). To obtain the hydroalcoholic extract, maceration in solvent extract ethanol PA 70% (v / v) was used. To determine the antifungal activity, the technique recommended by the International Clinical Laboratory Standard was used through the technique of Dilution in Broth and Sowing and Agar to determine the Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (CFM), respectively, front to strains of Aspergillus niger (ATCC 6275), Colletotrichum gloeosporioides (ATCC 96723), Penicillium chrysogenum (ATCC 10106). The results obtained for fungicidal action attested to CIM and strong inhibition for the action of essential oils and hydroalcoholic extracts with a concentration of 250 µg mL-1 in front of A. niger, C. gloeosporioides and P. chrysogenum. CFM's of 300, 250 and 500 mL-1 were observed in front of A. niger, C. gloeosporioides and P. chrysogenum, respectively. With the results obtained it is stated that a stable nanoemulsion was obtained for both (EX) and (OE) and that they present active compounds in which they favor an excellent antifungal activity.