Corynespora cassicola is a common fungal pathogen that affects various crops, leading to substantial economic losses in agriculture. The search for effective, safe, and environmentally friendly antifungal agents has intensified in recent years. This research paper investigates the antifungal activity of cinnamon oil against Corynespora isolated from watermelon seeds by agar plate method and explores its potential as a natural alternative to synthetic fungicides. The study involved in vitro experiment viz., Poisoned Food Technique to evaluate antifungal activity of different concentrations of cinnamon oil viz., 20%, 40%, 60%, 80% and 100% against Corynespora. The findings suggest that cinnamon oil exhibits potent antifungal properties, making it a promising candidate for controlling Corynespora and potentially other fungal pathogens in agriculture.