<p>Postharvest rots caused by <i>Fusarium pallidoroseum</i> and <i>Alternaria alternata</i> limit the commercialization of melons. Managing these diseases is crucial to ensure the quality of commercialized melons. The use of essential oils (EOs) and their constituents in the postharvest treatment of melons is a promising new to control those diseases. Therefore, this study aimed to evaluate the antifungal activity of different EOs on the mycelial growth of <i>F. pallidoroseum</i> and <i>A. alternata</i>, to determine the Minimum Inhibitory Concentration (MIC) and to analyze the chemical composition of the selected EOs by Gas Chromatography/Mass Spectrometry (GC–MS), as well as to evaluate the antifungal activity of their major constituents. According to the results, the EOs of cinnamon bark, oregano, rosemary pepper, and clove basil showed higher antifungal activity against the studied pathogens, with MIC ranging from 0.50 μL mL⁻¹ to 2.00 μL mL⁻¹. GC–MS analysis identified carvacrol, ρ-cymene, and thymol as the major constituents of oregano EO; in cinnamon bark EO, cinnamaldehyde, o-methoxy, and cinnamyl; in rosemary pepper EO, ​​thymol, ρ-cymene, and caryophyllene; and in clove basil EO, eugenol, ρ-cymene, and caryophyllene. The mixture of the three major constituents of each EO was more efficient than the pure EOs, with lower MIC value, ranging from 0.50 μL mL⁻¹ to 0.75 μL mL⁻¹. Therefore, using a mixture of major constituents of EOs has been demonstrated to be an efficient postharvest treatment to control rots in melon.</p>