In vitro study was carried out to assess the antifungal efficacy of methanolic extracts of aerial parts of Chenopodium murale L. against Fusarium oxysporum f. sp. cepae (FOC). This fungus causes basal rot disease in onion. Different concentrations (1.562 to 50 mg mL^-1) of leaf, stem and inflorescence of methanolic extracts of this weed were prepared in malt extract broth. Each tube (containing 1 mL growth media) was inoculated with 50 μL of FOC inoculum and incubated at 28 ºC for one week. Extracts of different parts showed variable results. Stem extract was the most effective where all the concentrations significantly suppressed growth of FOC by 25–59%. Leaf extract also showed profound antifungal activity where 6.25 mg mL^-1 and above concentrations significantly retarded the growth of FOC by 32–60%. The effect of inflorescence extract was insignificant. There was a linear regression between the extract concentration and fungal biomass. This study concludes that methanolic stem extract of C. murale is the most effective in controlling growth of FOC.