Abstract Crop residues are well known for their chemical (allelopathic) effects on crops. The allelopathic potential of the aqueous extracts and chopped residual of sorghum (Sorghum bicolor L.) on germination, seedling growth, relative water content, seedling dry weight, seedling length and antioxidant enzyme activity namely catalase (CAT), peroxidase (POD) and Superoxide Dismutase (SOD) of Silybum marianum was studied. Petri dish and pot experiments were performed in completely randomized design with three replications. Five concentrations of the aqueous extracts and foliar application of the sorghum [control (water distilled), 5, 10, 15 and 20 w/v] and sorghum chopped (0, 5, 10 and 20 g dry chopped / 100 g soil) were used in the experiments carried out in the laboratory and greenhouse, respectively. Petri dish trial showed that the different extract levels reduced total germination percentage (GP), germination rate (GR) and seedling growth. Moreover, relative water content (RWC), dry weight, and seedling length, antioxidant enzyme activity except CAT of milk thistle bioassay were inhibited when growth in soil incorporated with oven-chopped residual of sorghum. The inhibitory effects often depend on the concentration. Finally, sorghum residues had an enormous potential to suppress elements of germination and seedling growth of milk thistle. Hence, this soil incorporation of allelopathic crop residues could be employed as an important agent for crop rotation management.