The aim of this work was to determine (i) the antioxidant capacity of Thymus moroderi, Thymus piperella, Santolina chamaecyparissus, and Sideritis angustifolia essential oils (EOs) by means of four different antioxidant tests (the 2,2'-diphenyl-1-picrylhydrazyl radical scavenging method, the ferrous ion-chelating ability assay, the ferric reducing antioxidant power test, and the thiobarbituric acid reactive species test) and (ii) the antifungal activity against molds and yeast of these EOs by the agar dilution and the microdilution methods. T. piperella EO showed the lowest 50% inhibitory concentration by the 2,2'-diphenyl-1-picrylhydrazyl radical scavenging method (9.30 mg/ml) and by the thiobarbituric acid reactive species test (6.30 mg/ml) and the highest value by the ferric reducing antioxidant power test (2.64 Trolox equivalent antioxidant capacity), while S. chamaecyparissus showed the lowest 50% inhibitory concentration in the ferrous ion-chelating ability assay (3.94 mg/ml). All EOs had a substantial inhibitory effect on all assayed yeast strains. S. angustifolia EO had the lowest MICs (2.5 μl/ml) for the yeasts Saccharomyces cerevisiae, Debaryomyces hansenii, Rhodotorula mucilaginosa, and Pichia carsonii. As regards antifungal activity, S. angustifolia EO at high concentrations was the most effective EO in reducing the growth of Alternaria alternata, Penicillium chrysogenum, and Mucor racemosus, while S. chamaecyparissus was the best inhibitor of the molds Aspergillus flavus and Mucor circinelloides. The results obtained in this study suggest the possibility of using these essential oils as natural antioxidant food preservatives.