<p>Highly efficient modification of soil can enhance the stabilization of heavy metal ions. To explore the stabilization capacity of heavy metals in karst soil modified with plant decomposition solution (DS), DS with different decomposition times and concentrations from three plants was used to amend yellow–brown soil (YBS) from the karst area. The morphological properties of various modified YBSs were examinedusing scanning electron microscopy and Fourier transform infrared spectroscopy. The isothermal adsorption characteristics of Pb(II) and Cu(II) by different modified YBSs were investigated via the batch method, and the effects of temperature, pH, and ionic strength on Pb(II) and Cu(II) adsorption were compared. The results showed that the isothermal adsorption of Pb(II) and Cu(II) by the modified YBSs conformed to the Langmuir and Freudlich models, and the Langmuir model was more suitable to describe the adsorption process of Pb(II) and Cu(II). The maximum adsorption capacity (<i>q</i>_m) of Pb(II) and Cu(II) were 120.28–192.24 and 352.48–487.48&#xa0;mmol&#xa0;kg⁻¹, respectively. The <i>q</i>_m values of both Pb(II) and Cu(II) first increased and then decreased as the modification ratio of the decomposition solution (DS) increased, with the peak value observed at a modification ratio of 20%. A longer decomposition time of the DS for the modified YBSs was conducive to the adsorption of Pb(II) and Cu(II). Pb(II) and Cu(II) adsorption capacity increased with the increase of pH and temperature and the decrease of ionic strength. The adsorption of&#xa0;Pb(II) and Cu(II) by the modified YBSs was an endothermic, spontaneous, and entropy-adding reaction, and mainly dominated by chemical adsorption. The results suggested that the optimum adsorption conditions were pH = 6, ionic strength 0.05&#xa0;mol L⁻¹, and 40 ℃. Moreover, the YBS modified with DS was practical and eco-friendly for heavy metals treatment.</p>