Abstract: Double dilution method was applied to detect variable roles in anti-microorganism of 7 bacteria by measuring the minimal inhibitory concentration (MIC) in 18 genotypes of Senecio scandens Buch-Ham. Our results indicated that diverse values of MIC could be attributed to dif-ferent species of bacteria, as well as genotypes of S. scandens. Namely, more efficient capability of antibacterial role was detected in Staphylococcus aureus than in Pseudomonas aeruginosa 4 and 6 different scores of MIC were measured in Aeromonas sobria and Edwardsiella tarda, re-spectively. As compared with A. sobria and E. tarda,5 variable measurements were detected in S. aureus,P, aeruginosa, Escherichia coil, Salmonella paratyphi, and Shigella flexneri. The authors argued that complex component should be contributed to antibacterial roles. The results in the present study suggested that antibacterial character should be controlled by quantitative trait loci.