Fungal diseases account for more than 80% of total diseases that affect crops annually. Early blight, one of the most important diseases of tomato, is caused by the fungal pathogen Alternaria solani. The disease is hard to prevent and leads to significant yield losses. Chemical fungicides remain the only way to control it. Nonetheless, their excessive use has led to the appearance of more aggressive strains of A. solani in addition to various environmental and health issues. There is therefore an urgent need to find safe and durable alternatives to control early blight. Essential oils are plant compounds that have strong antimicrobial properties. In this project, we tested the ability of peppermint oil, thyme oil, Eucalyptus oil, cardamom oil, coriander oil and clove oil to inhibit the growth of A. solani in vitro and control early blight disease in tomato plants. The data collected showed that all six essential oils had strong antifungal activity against A. solani. Since thyme oil and peppermint oil displayed the strongest antifungal activity, we sprayed either oil on six weeks tomato plants before inoculating them with spores of A. solani. We then assessed the severity of early blight disease in treated and control plants. The results showed that the plants treated with either peppermint oil or thyme oils were resistant to A. solani and did not develop early blight disease symptoms. These data indicate that these two oils can be used as an alternative to chemical fungicides in controlling early blight disease.