Using synthetic chemicals to control fungi is cost-effective, non environmentally friendly, toxic to humans, and causes pollution to the water bodies. The research for biodegradable, non-toxic to humans, and economically viable for controlling fungi infection led to using traditional plants. Allium sativum has fungicidal activities against various organisms. The aim of this research is to determine the efficacy of the aqueous extract of Allium sativum flower against groundnut stem rot pathogen. The infected groundnut was obtained from various farms; the fungus was isolated and identified. The in vitro antifungal activity and its pathogenicity were also determined. The fungal Sclerotium rolfsii was isolated from the infected ground nut. The certified ground nut was planted on the sterile soil. The germinated seedlings were sprinkled with the pure isolate of Sclerotium rolfsii and the symptoms of the infection were observed. The organism was isolated from the infected leaves and stems. The anti-fungal activity of the extract of 20, 40, 60, and 80 % of Allium sativum flower aqueous extract shows significant inhibition on the mycelial growth of Sclerotium rolfsii. The Allium sativum flower aqueous extract has shown promising inhibitory effects against Sclerotium rolfsii.