Rhizoctonia solani Kühn is a broad host ranged soil-borne pathogen that infects more than 200 plant species. This study was carried out to assess the antifungal potential of stem extract of a solanaceous weed Sonchus asper (L.) Hill and to identify possible antifungal compounds using GC–MS method. In a laboratory bioassay, the methanolic stem extract at concentrations of 100 and 200 mg mL⁻¹ significantly inhibited fungal growth by 77% and 81%, respectively. The extract was subsequently subjected to GC–MS analysis, which identified 49 compounds. The predominant compound was benzoic acid, 4-hydroxy-3-methoxy-, methyl ester (15.65%), followed by D-ribofuranose, 5-deoxy-5-(methylsulfinyl) (13.68%), phenol, 4-ethenyl-2,6-dimethoxy- (8.98%), and 4-hydroxy-2,2′,4′,6′-tetrachlorobiphenyl (7.19%). Literature survey showed that compounds such as benzoic acid, 4-hydroxy-3-methoxy-, methyl ester; 10-undecenoic acid, pyridine, 2-pentyl-;   9-octadecenoic acid, (E)-; cetene; azelaic acid; and octanoic acid possess antifungal potential against a variety of humans and plants fungal pathogens. These findings indicate that S. asper stem extract exhibits antifungal activity against R. solani and may serve as a source of candidate antifungal compounds. More studies are required to validate the antifungal activity of individual compounds, establish their mechanisms of action, and evaluate their potential application in plant disease management.