Four herbaceous plants, gramineae weeds (Digitaria ciliaris, Echinochloa crusgali) and composite weeds (Eclipta prostrata, Crassocephalum crepidioides) distributed in the red soils of the South China, were used to examine activity of root border cells, root relative elongation, levels of aluminum, proline, malondialdehyde (MDA), and membrane permeability (MP) in the Al-treated roots. It was found that activity of root border cells was significantly decreased with increasing Al3+ concentrations or treatment time in these four weeds. The decreasing magnitude was higher in composite weeds than in gramineae weeds, while the contents of aluminum, proline and MDA, and membrane permeability were increased in the roots. Further analysis showed that root growth was more markedly inhibited by Al in Eclipta prostrata and Crassocephalum crepidioides than in Digitaria ciliaris and Echinochloa crusgali under the same conditions. The contents of aluminum, proline and MDA, and membrane permeability in these four weeds roots reached a maximum at 1000 mg?L-1 Al3+ concentrations, while the increase in Digitaria ciliaris and Echinochloa crusgali were less than in Eclipta prostrata and Crassocephalum crepidioides. No significant increase was observed on contents of proline and MDA in gramineae weeds roots among the different exterior Al3+ levels (P>0.05). These findings suggested that the damage levels of aluminum to these four weeds were enhanced with increasing Al concentrations and exposure time; However, the relatively higher activity of the root border cells, longer root relative elongation, lower levels of aluminum, proline, MDA and MP improved the tolerance to Al stress in Digitaria ciliaris and Echinochloa crusgali. Gramineae weeds(Digitaria ciliaris, Echinochloa crusgali) were more resistant to Al toxicity than composite weeds(Eclipta prostrata, Crassocephalum crepidioides).