The antifungal activities of 19 plant essential oils against six wood mold and stain fungi (Aspergillus niger, Penicillium citrinum, Trichoderma viride, Botryodiplodia theobromae, Fusarium moniliforme, and Alternaria alternata) were investigated with the in vitro medium method. The chemical compositions and volatilization rates of the essential oils were analyzed by gas chromatography–mass spectrometry and oven heating, respectively. Antifungal effects of the essential oils on fresh Pinus massoniana wood were evaluated by dipping treatment. The average antifungal efficacies of the essential oils varied from 0.1 to 1.0, and oils of Cinnamomum cassia, Syzygium aromaticum, and Thymus mongolicus showed the greatest antifungal activities and completely inhibited the growth of all six fungi. The essential oils presented great differences in their main chemical components, and a significant negative linear correlation (Pearson correlation coefficient = -0.627, p < 0.01) was found between antifungal efficacy and volatilization rate, indicating that both chemical composition and volatilization rate are important factors influencing the antifungal activities of essential oils. Eight essential oils effectively inhibited the growth of fungi in Pinus massoniana wood with an absorption of 65.51 g/m2 ± 13.78 g/m2, and they have the potential to be environmentally friendly anti-mildew agents.