Ocimum gratissimum L. or clove basil, belongs to the Lamiaceae family, has various desirable uses and applications. Beyond its aromatic, seasoning, and medicinal applications, this plant also has antimicrobial activity. This study was aimed at assessing the antifungal activity, yield, and composition of the essential oil (EO) of O. gratissimum. The species was cultivated in garden beds with dystrophic red latosol soil type containing high organic-matter content. The EO was obtained by hydrodistillation of dried leaves in a modified Clevenger apparatus, followed by determination of its content. Chemical characterization was carried out by gas chromatography-mass spectrometry (GC-MS). Microbial activity was assessed using the broth microdilution method, by determining the minimum inhibitory concentration (MIC), in order to compare the antimicrobial effect of EO in 10 isolates-Fusarium oxysporum f. sp tracheiphilum (CMM-0033), F. oxysporum f. sp. cubense (CMM-0813 and CMM-2819), F. oxysporum f. sp lycopersici (CMM-1104), F. solani (CMM-3828), Rhizoctonia solani (CMM-3274), and Macrophomina phaseolina (CMM-2715, CMM-3875, CMM-3615, and CMM-3650). The EO was a highly effective inhibitor of the studied phytopathogenic fungi, with MICs varying from 31.25 to 125 µg/mL. F. oxysporum f. sp lycopersici and R. solani were the most sensitive; both were inhibited at an MIC of 31.25 µg/mL. The EO content in the plant extract was 0.18%. Thirty chemical compounds were detected via GC-MS, with linalool (32.9%) being the major compound followed by 1,8-cineole (21.9%), both oxygenated monoterpenes. It can be concluded that clove basil EO is a highly effective antifungal agent, and therefore, a potential alternative for the control of plant pathogenic diseases.