Alternaria alternata (Fries) Keissler, is one of the major fungal pathogen of grapes (Vitis vinefera L.) responsible for fruit malformation and influences the fruit quality during handling, transportation, and distribution. The current study was performed to investigate the effectiveness of some plant essential oils (EOs) against Alternaria alternata causing bunch rot of grapes. For this purpose, thyme (Thymus vulgare L.), fennel (Foeniculum vulgare L.), garlic (Allium sativum L.), ginger (Zingiber officinale L.) and carum (Carum capticum L.) essential oils at 0.04, 0.06, 0.08 and 0.1% concentrations were evaluated in vitro against this pathogen. All experiments were set up in a complete randomized design (CRD) with three replications. In addition, among the tested materials for controlling A. alternata, thyme essential oil at all applied concentrations significantly reduced the fungal growth. Furthermore, the experiments related to reducing the decay development and average weight loss percentage of grapes cv. Perlette revealed similar results regarding thyme essential oil efficacy. Thyme EO did not exhibited any phytotoxic effects on the fruit peel. Therefore, after long term and wide-ranging trial thyme essential oil could be recommended as a potential source of eco-friendly botanical fungicide against A. alternata.